diff --git a/xunit.runner.wpf/ITestUtil.cs b/xunit.runner.wpf/ITestUtil.cs
index e6566ba..35f786a 100644
--- a/xunit.runner.wpf/ITestUtil.cs
+++ b/xunit.runner.wpf/ITestUtil.cs
@@ -1,14 +1,9 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
-using System.Collections.ObjectModel;
-using System.Linq;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
-using System.Windows.Threading;
 using xunit.runner.data;
-using xunit.runner.wpf.ViewModel;
 
 namespace xunit.runner.wpf
 {
@@ -17,16 +12,16 @@ namespace xunit.runner.wpf
         /// <summary>
         /// Discover the list of test cases which are available in the specified assembly.
         /// </summary>
-        Task Discover(string assemblyPath, Action<List<TestCaseData>> callback, CancellationToken cancellationToken = default(CancellationToken));
+        Task Discover(string assemblyPath, Action<IEnumerable<TestCaseData>> callback, CancellationToken cancellationToken = default(CancellationToken));
 
         /// <summary>
         /// Begin a run of all unit tests for the given assembly.
         /// </summary>
-        Task RunAll(string assemblyPath, Action<List<TestResultData>> callback, CancellationToken cancellationToken = default(CancellationToken));
+        Task RunAll(string assemblyPath, Action<IEnumerable<TestResultData>> callback, CancellationToken cancellationToken = default(CancellationToken));
 
         /// <summary>
         /// Begin a run of specific unit tests for the given assembly.
         /// </summary>
-        Task RunSpecific(string assemblyPath, ImmutableArray<string> testCaseDisplayNames, Action<List<TestResultData>> callback, CancellationToken cancellationToken = default(CancellationToken));
+        Task RunSpecific(string assemblyPath, ImmutableArray<string> testCaseDisplayNames, Action<IEnumerable<TestResultData>> callback, CancellationToken cancellationToken = default(CancellationToken));
     }
 }
diff --git a/xunit.runner.wpf/Impl/RemoteTestUtil.cs b/xunit.runner.wpf/Impl/RemoteTestUtil.cs
index aa94034..64dbabe 100644
--- a/xunit.runner.wpf/Impl/RemoteTestUtil.cs
+++ b/xunit.runner.wpf/Impl/RemoteTestUtil.cs
@@ -3,15 +3,11 @@ using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
-using System.IO;
 using System.IO.Pipes;
-using System.Linq;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Windows.Threading;
 using xunit.runner.data;
-using xunit.runner.wpf.ViewModel;
 
 namespace xunit.runner.wpf.Impl
 {
@@ -137,17 +133,17 @@ namespace xunit.runner.wpf.Impl
 
         #region ITestUtil
 
-        Task ITestUtil.Discover(string assemblyPath, Action<List<TestCaseData>> callback, CancellationToken cancellationToken)
+        Task ITestUtil.Discover(string assemblyPath, Action<IEnumerable<TestCaseData>> callback, CancellationToken cancellationToken)
         {
             return Discover(assemblyPath, callback, cancellationToken);
         }
 
-        Task ITestUtil.RunAll(string assemblyPath, Action<List<TestResultData>> callback, CancellationToken cancellationToken)
+        Task ITestUtil.RunAll(string assemblyPath, Action<IEnumerable<TestResultData>> callback, CancellationToken cancellationToken)
         {
             return RunCore(Constants.ActionRunAll, assemblyPath, ImmutableArray<string>.Empty, callback, cancellationToken);
         }
 
-        Task ITestUtil.RunSpecific(string assemblyPath, ImmutableArray<string> testCaseDisplayNames, Action<List<TestResultData>> callback, CancellationToken cancellationToken)
+        Task ITestUtil.RunSpecific(string assemblyPath, ImmutableArray<string> testCaseDisplayNames, Action<IEnumerable<TestResultData>> callback, CancellationToken cancellationToken)
         {
             return RunCore(Constants.ActionRunSpecific, assemblyPath, testCaseDisplayNames, callback, cancellationToken);
         }
diff --git a/xunit.runner.wpf/ViewModel/MainViewModel.cs b/xunit.runner.wpf/ViewModel/MainViewModel.cs
index c79b0f9..1d1f249 100644
--- a/xunit.runner.wpf/ViewModel/MainViewModel.cs
+++ b/xunit.runner.wpf/ViewModel/MainViewModel.cs
@@ -477,57 +477,42 @@ namespace xunit.runner.wpf.ViewModel
             }
         }
 
-        private void OnTestDiscovered(List<TestCaseData> testCaseDataList)
+        private void OnTestDiscovered(IEnumerable<TestCaseData> testCases)
         {
-            var allTraits = new SortedDictionary<string, SortedSet<string>>();
-            foreach (var data in testCaseDataList)
+            var traitWorkerList = new List<TraitViewModel>();
+
+            foreach (var testCase in testCases)
             {
-                AddTraits(allTraits, data);
-            }
+                traitWorkerList.Clear();
 
-            this.allTestCases.AddRange(testCaseDataList.Select(d =>
-                new TestCaseViewModel(d.DisplayName, d.AssemblyPath, Convert(CreateSortedTraits(d)))));
-
-            this.traitCollectionView.AddRange(Convert(allTraits));
-        }
-
-        private SortedDictionary<string, SortedSet<string>> CreateSortedTraits(TestCaseData data)
-        {
-            var traits = new SortedDictionary<string, SortedSet<string>>();
-            AddTraits(traits, data);
-            return traits;
-        }
-
-        private static IEnumerable<TraitViewModel> Convert(SortedDictionary<string, SortedSet<string>> allTraits)
-        {
-            foreach (var trait in allTraits)
-            {
-                var name = trait.Key;
-                var values = trait.Value;
-
-                var viewModel = new TraitViewModel(name);
-                viewModel.AddValues(values);
-
-                yield return viewModel;
-            }
-        }
-
-        private static void AddTraits(SortedDictionary<string, SortedSet<string>> allTraits, TestCaseData data)
-        {
-            foreach (var kvp in data.TraitMap)
-            {
-                SortedSet<string> values;
-                if (!allTraits.TryGetValue(kvp.Key, out values))
+                // Get or create traits.
+                if (testCase.TraitMap?.Count > 0)
                 {
-                    values = new SortedSet<string>();
-                    allTraits.Add(kvp.Key, values);
+                    foreach (var kvp in testCase.TraitMap)
+                    {
+                        var name = kvp.Key;
+                        var values = kvp.Value;
+
+                        var parentTraitViewModel = traitCollectionView.GetOrAdd(name);
+
+                        foreach (var value in values)
+                        {
+                            var traitViewModel = parentTraitViewModel.GetOrAdd(value);
+                            traitWorkerList.Add(traitViewModel);
+                        }
+                    }
                 }
 
-                values.AddRange(kvp.Value);
+                var testCaseViewModel = new TestCaseViewModel(
+                    testCase.DisplayName,
+                    testCase.AssemblyPath,
+                    traitWorkerList);
+
+                this.allTestCases.Add(testCaseViewModel);
             }
         }
 
-        private void OnTestFinished(List<TestResultData> testResultData)
+        private void OnTestFinished(IEnumerable<TestResultData> testResultData)
         {
             foreach (var data in testResultData)
             {
diff --git a/xunit.runner.wpf/ViewModel/TraitCollectionView.cs b/xunit.runner.wpf/ViewModel/TraitCollectionView.cs
index fb5610b..ef5297b 100644
--- a/xunit.runner.wpf/ViewModel/TraitCollectionView.cs
+++ b/xunit.runner.wpf/ViewModel/TraitCollectionView.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Linq;
 
@@ -26,6 +27,20 @@ namespace xunit.runner.wpf.ViewModel
             }
         }
 
+        public TraitViewModel GetOrAdd(string text)
+        {
+            var index = this.Collection.BinarySearch(text, StringComparer.Ordinal, vm => vm.Text);
+
+            if (index < 0)
+            {
+                var viewModel = new TraitViewModel(text);
+                this.Collection.Insert(~index, viewModel);
+                return viewModel;
+            }
+
+            return this.Collection[index];
+        }
+
         public ISet<TraitViewModel> GetCheckedTraits()
         {
             return new HashSet<TraitViewModel>(
diff --git a/xunit.runner.wpf/ViewModel/TraitViewModel.cs b/xunit.runner.wpf/ViewModel/TraitViewModel.cs
index 526bfdd..8854415 100644
--- a/xunit.runner.wpf/ViewModel/TraitViewModel.cs
+++ b/xunit.runner.wpf/ViewModel/TraitViewModel.cs
@@ -87,6 +87,20 @@ namespace xunit.runner.wpf.ViewModel
             }
         }
 
+        public TraitViewModel GetOrAdd(string text)
+        {
+            var index = this.Children.BinarySearch(text, StringComparer.Ordinal, vm => vm.Text);
+
+            if (index < 0)
+            {
+                var viewModel = new TraitViewModel(this, text);
+                this.Children.Insert(~index, viewModel);
+                return viewModel;
+            }
+
+            return this.Children[index];
+        }
+
         public bool? IsChecked
         {
             get { return _isChecked; }