diff --git a/Octokit.Tests.Integration/Clients/PullRequestsClientTests.cs b/Octokit.Tests.Integration/Clients/PullRequestsClientTests.cs
index 3bee5479..77b6773a 100644
--- a/Octokit.Tests.Integration/Clients/PullRequestsClientTests.cs
+++ b/Octokit.Tests.Integration/Clients/PullRequestsClientTests.cs
@@ -259,7 +259,11 @@ public class PullRequestsClientTests : IDisposable
             });
         }
 
-        var newTree = new NewTree { Tree = collection };
+        var newTree = new NewTree();
+        foreach (var item in collection)
+        {
+            newTree.Tree.Add(item);
+        }
 
         return await _client.GitDatabase.Tree.Create(Helper.UserName, _repository.Name, newTree);
     }
diff --git a/Octokit.Tests.Integration/Clients/RepositoryCommitsClientTests.cs b/Octokit.Tests.Integration/Clients/RepositoryCommitsClientTests.cs
index 49374bba..35040390 100644
--- a/Octokit.Tests.Integration/Clients/RepositoryCommitsClientTests.cs
+++ b/Octokit.Tests.Integration/Clients/RepositoryCommitsClientTests.cs
@@ -190,7 +190,11 @@ public class RepositoryCommitsClientTests
                 });
             }
 
-            var newTree = new NewTree { Tree = collection };
+            var newTree = new NewTree();
+            foreach (var item in collection)
+            {
+                newTree.Tree.Add(item);
+            }
 
             return await _client.GitDatabase.Tree.Create(Helper.UserName, _repository.Name, newTree);
         }
diff --git a/Octokit.Tests.Integration/Helpers/RepositorySetupHelper.cs b/Octokit.Tests.Integration/Helpers/RepositorySetupHelper.cs
index 97db3c00..1a9147af 100644
--- a/Octokit.Tests.Integration/Helpers/RepositorySetupHelper.cs
+++ b/Octokit.Tests.Integration/Helpers/RepositorySetupHelper.cs
@@ -27,7 +27,11 @@ namespace Octokit.Tests.Integration.Helpers
                 });
             }
 
-            var newTree = new NewTree { Tree = collection };
+            var newTree = new NewTree();
+            foreach (var item in collection)
+            {
+                newTree.Tree.Add(item);
+            }
 
             return await client.GitDatabase.Tree.Create(repository.Owner.Login, repository.Name, newTree);
         }
diff --git a/Octokit/Models/Request/NewTree.cs b/Octokit/Models/Request/NewTree.cs
index 97b6e940..d88b177d 100644
--- a/Octokit/Models/Request/NewTree.cs
+++ b/Octokit/Models/Request/NewTree.cs
@@ -23,8 +23,7 @@ namespace Octokit
         /// <summary>
         /// The list of Tree Items for this new Tree item.
         /// </summary>
-        [SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
-        public ICollection<NewTreeItem> Tree { get; set; }
+        public ICollection<NewTreeItem> Tree { get; private set; }
 
         internal string DebuggerDisplay
         {