diff --git a/src/vs/base/browser/ui/tree/treeModel.ts b/src/vs/base/browser/ui/tree/treeModel.ts
index 2f352c42ac1e3d27f749ece0ab7fd3ad9cfab11d..20ede7b260c9c0bb4461264c9313be4817d8738d 100644
--- a/src/vs/base/browser/ui/tree/treeModel.ts
+++ b/src/vs/base/browser/ui/tree/treeModel.ts
@@ -133,7 +133,8 @@ export class TreeModel<T, TFilterData = void> {
 		const lastIndex = location[location.length - 1];
 		const deletedNodes = parentNode.children.splice(lastIndex, deleteCount, ...nodesToInsert);
 		const visibleDeleteCount = deletedNodes.reduce((r, node) => r + node.revealedCount, 0);
-		parentNode.revealedCount += revealedCount - visibleDeleteCount;
+
+		this._updateAncestorsRevealedCount(parentNode, revealedCount - visibleDeleteCount);
 
 		if (revealed) {
 			this.list.splice(listIndex, visibleDeleteCount, treeListElementsToInsert);
diff --git a/src/vs/base/browser/ui/tree/treeObjectModel.ts b/src/vs/base/browser/ui/tree/treeObjectModel.ts
index 74ac3214ee8e1817e83c799611468c3b26bfa414..46affafd041d38a3417df14c8d161ab6b69e0c5b 100644
--- a/src/vs/base/browser/ui/tree/treeObjectModel.ts
+++ b/src/vs/base/browser/ui/tree/treeObjectModel.ts
@@ -14,6 +14,8 @@ export class TreeObjectModel<T extends NonNullable<any>, TFilterData = void> {
 	private model: TreeModel<T, TFilterData>;
 	private nodes = new Map<T, ITreeNode<T, TFilterData>>();
 
+	get size(): number { return this.nodes.size; }
+
 	constructor(list: ISpliceable<ITreeNode<T, TFilterData>>, options: ITreeModelOptions<T, TFilterData> = {}) {
 		this.model = new TreeModel(list, options);
 	}
diff --git a/src/vs/base/test/browser/ui/tree/treeObjectModel.test.ts b/src/vs/base/test/browser/ui/tree/treeObjectModel.test.ts
new file mode 100644
index 0000000000000000000000000000000000000000..b2ed750edcf9419e4fc83c3fcbb3502652ed3f9b
--- /dev/null
+++ b/src/vs/base/test/browser/ui/tree/treeObjectModel.test.ts
@@ -0,0 +1,100 @@
+/*---------------------------------------------------------------------------------------------
+ *  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 { ITreeNode } from 'vs/base/browser/ui/tree/treeModel';
+import { ISpliceable } from 'vs/base/common/sequence';
+import { TreeObjectModel } from 'vs/base/browser/ui/tree/treeObjectModel';
+import { Iterator } from 'vs/base/common/iterator';
+
+function toSpliceable<T>(arr: T[]): ISpliceable<T> {
+	return {
+		splice(start: number, deleteCount: number, elements: T[]): void {
+			arr.splice(start, deleteCount, ...elements);
+		}
+	};
+}
+
+function toArray<T>(list: ITreeNode<T>[]): T[] {
+	return list.map(i => i.element);
+}
+
+suite('TreeObjectModel', function () {
+
+	test('ctor', () => {
+		const list = [] as ITreeNode<number>[];
+		const model = new TreeObjectModel<number>(toSpliceable(list));
+		assert(model);
+		assert.equal(list.length, 0);
+		assert.equal(model.size, 0);
+	});
+
+	test('flat', () => {
+		const list = [] as ITreeNode<number>[];
+		const model = new TreeObjectModel<number>(toSpliceable(list));
+
+		model.splice(null, 0, 0, Iterator.fromArray([
+			{ element: 0 },
+			{ element: 1 },
+			{ element: 2 }
+		]));
+
+		assert.deepEqual(toArray(list), [0, 1, 2]);
+		assert.equal(model.size, 3);
+
+		model.splice(null, 3, 0, Iterator.fromArray([
+			{ element: 3 },
+			{ element: 4 },
+			{ element: 5 },
+		]));
+
+		assert.deepEqual(toArray(list), [0, 1, 2, 3, 4, 5]);
+		assert.equal(model.size, 6);
+
+		model.splice(null, 2, 2);
+		assert.deepEqual(toArray(list), [0, 1, 4, 5]);
+		assert.equal(model.size, 4);
+	});
+
+	test('nested', () => {
+		const list = [] as ITreeNode<number>[];
+		const model = new TreeObjectModel<number>(toSpliceable(list));
+
+		model.splice(null, 0, 0, Iterator.fromArray([
+			{
+				element: 0, children: Iterator.fromArray([
+					{ element: 10 },
+					{ element: 11 },
+					{ element: 12 },
+				])
+			},
+			{ element: 1 },
+			{ element: 2 }
+		]));
+
+		assert.deepEqual(toArray(list), [0, 10, 11, 12, 1, 2]);
+		assert.equal(model.size, 6);
+
+		model.splice(12, 0, 0, Iterator.fromArray([
+			{ element: 120 },
+			{ element: 121 }
+		]));
+
+		assert.deepEqual(toArray(list), [0, 10, 11, 12, 120, 121, 1, 2]);
+		assert.equal(model.size, 8);
+
+		model.splice(0, 1, 1);
+		assert.deepEqual(toArray(list), [0, 10, 12, 120, 121, 1, 2]);
+		assert.equal(model.size, 7);
+
+		model.splice(null, 0, 1);
+		assert.deepEqual(toArray(list), [1, 2]);
+		assert.equal(model.size, 2);
+
+		model.splice(null, 0, 2);
+		assert.deepEqual(toArray(list), []);
+		assert.equal(model.size, 0);
+	});
+});
\ No newline at end of file