Using a HashSet at the right time.

                       Method |     Mean |     Error |    StdDev |
----------------------------- |---------:|----------:|----------:|
 OriginalTreeBuilderBenchmark | 61.32 ms | 0.8018 ms | 0.7500 ms |
  CurrentTreeBuilderBenchmark | 42.24 ms | 0.8295 ms | 1.0786 ms |

Author: StanleyGoldman

src/GitHub.Api/UI/TreeBuilder.cs

@@ -76,10 +76,12 @@ internal static FileTreeNode BuildTreeRoot(IList<GitStatusEntry> newEntries, Lis
         {
             Guard.ArgumentNotNullOrEmpty(newEntries, "newEntries");
 
+            var newEntriesSetByPath = new HashSet<string>(newEntries.Select(entry => entry.Path));
+
             // Remove what got nuked
             for (var index = 0; index < gitStatusEntries.Count;)
             {
-                if (!newEntries.Contains(gitStatusEntries[index]))
+                if (!newEntriesSetByPath.Contains(gitStatusEntries[index].Path))
                 {
                     gitStatusEntries.RemoveAt(index);
                     gitCommitTargets.RemoveAt(index);