diff --git a/src/vs/workbench/common/views.ts b/src/vs/workbench/common/views.ts
index c00cef45a27..39e05d7fe73 100644
--- a/src/vs/workbench/common/views.ts
+++ b/src/vs/workbench/common/views.ts
@@ -24,6 +24,7 @@ import Severity from 'vs/base/common/severity';
 import { IPaneComposite } from 'vs/workbench/common/panecomposite';
 import { IAccessibilityInformation } from 'vs/platform/accessibility/common/accessibility';
 import { IMarkdownString } from 'vs/base/common/htmlContent';
+import { mixin } from 'vs/base/common/objects';
 
 export const TEST_VIEW_CONTAINER_ID = 'workbench.view.extension.test';
 
@@ -650,9 +651,9 @@ export interface ITreeItem {
 }
 
 export class ResolvableTreeItem implements ITreeItem {
-	handle: string;
+	handle!: string;
 	parentHandle?: string;
-	collapsibleState: TreeItemCollapsibleState;
+	collapsibleState!: TreeItemCollapsibleState;
 	label?: ITreeItemLabel;
 	description?: string | boolean;
 	icon?: UriComponents;
@@ -668,20 +669,7 @@ export class ResolvableTreeItem implements ITreeItem {
 	private resolved: boolean = false;
 	private _hasResolve: boolean = false;
 	constructor(treeItem: ITreeItem, resolve?: (() => Promise<ITreeItem | undefined>)) {
-		this.handle = treeItem.handle;
-		this.parentHandle = treeItem.parentHandle;
-		this.collapsibleState = treeItem.collapsibleState;
-		this.label = treeItem.label;
-		this.description = treeItem.description;
-		this.icon = treeItem.icon;
-		this.iconDark = treeItem.iconDark;
-		this.themeIcon = treeItem.themeIcon;
-		this.resourceUri = treeItem.resourceUri;
-		this.tooltip = treeItem.tooltip;
-		this.contextValue = treeItem.contextValue;
-		this.command = treeItem.command;
-		this.children = treeItem.children;
-		this.accessibilityInformation = treeItem.accessibilityInformation;
+		mixin(this, treeItem);
 		this._hasResolve = !!resolve;
 		this.resolve = async () => {
 			if (resolve && !this.resolved) {
diff --git a/src/vs/workbench/test/browser/api/mainThreadTreeViews.test.ts b/src/vs/workbench/test/browser/api/mainThreadTreeViews.test.ts
new file mode 100644
index 00000000000..936a51b094f
--- /dev/null
+++ b/src/vs/workbench/test/browser/api/mainThreadTreeViews.test.ts
@@ -0,0 +1,86 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as assert from 'assert';
+import { ExtHostTreeViewsShape, IExtHostContext } from 'vs/workbench/api/common/extHost.protocol';
+import { mock } from 'vs/base/test/common/mock';
+import { ITreeItem, IViewsRegistry, Extensions, ViewContainerLocation, IViewContainersRegistry, ITreeViewDescriptor, ITreeView, ViewContainer, IViewDescriptorService, TreeItemCollapsibleState } from 'vs/workbench/common/views';
+import { NullLogService } from 'vs/platform/log/common/log';
+import { MainThreadTreeViews } from 'vs/workbench/api/browser/mainThreadTreeViews';
+import { TestViewsService, workbenchInstantiationService } from 'vs/workbench/test/browser/workbenchTestServices';
+import { TestExtensionService } from 'vs/workbench/test/common/workbenchTestServices';
+import { TestNotificationService } from 'vs/platform/notification/test/common/testNotificationService';
+import { Registry } from 'vs/platform/registry/common/platform';
+import { SyncDescriptor } from 'vs/platform/instantiation/common/descriptors';
+import { TestInstantiationService } from 'vs/platform/instantiation/test/common/instantiationServiceMock';
+import { CustomTreeView } from 'vs/workbench/contrib/views/browser/treeView';
+import { ViewDescriptorService } from 'vs/workbench/services/views/browser/viewDescriptorService';
+
+suite('MainThreadHostTreeView', function () {
+	const testTreeViewId = 'testTreeView';
+	const customValue = 'customValue';
+	const ViewsRegistry = Registry.as<IViewsRegistry>(Extensions.ViewsRegistry);
+
+	interface CustomTreeItem extends ITreeItem {
+		customProp: string;
+	}
+
+	class MockExtHostTreeViewsShape extends mock<ExtHostTreeViewsShape>() {
+		async $getChildren(treeViewId: string, treeItemHandle?: string): Promise<ITreeItem[]> {
+			return [<CustomTreeItem>{ handle: 'testItem1', collapsibleState: TreeItemCollapsibleState.Expanded, customProp: customValue }];
+		}
+
+		async $hasResolve(): Promise<boolean> {
+			return false;
+		}
+
+		$setVisible(): void { }
+	}
+
+	let container: ViewContainer;
+	let mainThreadTreeViews: MainThreadTreeViews;
+	let extHostTreeViewsShape: MockExtHostTreeViewsShape;
+
+	setup(async () => {
+		const instantiationService: TestInstantiationService = <TestInstantiationService>workbenchInstantiationService();
+		const viewDescriptorService = instantiationService.createInstance(ViewDescriptorService);
+		instantiationService.stub(IViewDescriptorService, viewDescriptorService);
+		container = Registry.as<IViewContainersRegistry>(Extensions.ViewContainersRegistry).registerViewContainer({ id: 'testContainer', name: 'test', ctorDescriptor: new SyncDescriptor(<any>{}) }, ViewContainerLocation.Sidebar);
+		const viewDescriptor: ITreeViewDescriptor = {
+			id: testTreeViewId,
+			ctorDescriptor: null!,
+			name: 'Test View 1',
+			treeView: instantiationService.createInstance(CustomTreeView, 'testTree', 'Test Title'),
+		};
+		ViewsRegistry.registerViews([viewDescriptor], container);
+
+		const testExtensionService = new TestExtensionService();
+		extHostTreeViewsShape = new MockExtHostTreeViewsShape();
+		mainThreadTreeViews = new MainThreadTreeViews(
+			new class implements IExtHostContext {
+				remoteAuthority = '';
+				assertRegistered() { }
+				set(v: any): any { return null; }
+				getProxy(): any {
+					return extHostTreeViewsShape;
+				}
+			}, new TestViewsService(), new TestNotificationService(), testExtensionService, new NullLogService());
+		mainThreadTreeViews.$registerTreeViewDataProvider(testTreeViewId, { showCollapseAll: false, canSelectMany: false });
+		await testExtensionService.whenInstalledExtensionsRegistered();
+	});
+
+	teardown(() => {
+		ViewsRegistry.deregisterViews(ViewsRegistry.getViews(container), container);
+	});
+
+	test('getChildren keeps custom properties', async () => {
+		const treeView: ITreeView = (<ITreeViewDescriptor>ViewsRegistry.getView(testTreeViewId)).treeView;
+		const children = await treeView.dataProvider?.getChildren({ handle: 'root', collapsibleState: TreeItemCollapsibleState.Expanded });
+		assert(children!.length === 1, 'Exactly one child should be returned');
+		assert((<CustomTreeItem>children![0]).customProp === customValue, 'Tree Items should keep custom properties');
+	});
+
+
+});