diff --git a/src/vs/vscode.d.ts b/src/vs/vscode.d.ts
index 6588af1c28c..71329e06fea 100644
--- a/src/vs/vscode.d.ts
+++ b/src/vs/vscode.d.ts
@@ -6155,7 +6155,7 @@ declare module 'vscode' {
 		/**
 		 * Element that is expanded or collapsed.
 		 */
-		element: T;
+		readonly element: T;
 
 	}
 
@@ -6167,7 +6167,7 @@ declare module 'vscode' {
 		/**
 		 * Selected elements.
 		 */
-		selection: T[];
+		readonly selection: T[];
 
 	}
 
@@ -6179,7 +6179,7 @@ declare module 'vscode' {
 		/**
 		 * `true` if the [tree view](#TreeView) is visible otherwise `false`.
 		 */
-		visible: boolean;
+		readonly visible: boolean;
 
 	}
 
diff --git a/src/vs/workbench/api/node/extHostTreeViews.ts b/src/vs/workbench/api/node/extHostTreeViews.ts
index 2df9b9076cd..19b4b163334 100644
--- a/src/vs/workbench/api/node/extHostTreeViews.ts
+++ b/src/vs/workbench/api/node/extHostTreeViews.ts
@@ -199,9 +199,9 @@ class ExtHostTreeView<T> extends Disposable {
 		const element = this.getExtensionElement(treeItemHandle);
 		if (element) {
 			if (expanded) {
-				this._onDidExpandElement.fire({ element });
+				this._onDidExpandElement.fire(Object.freeze({ element }));
 			} else {
-				this._onDidCollapseElement.fire({ element });
+				this._onDidCollapseElement.fire(Object.freeze({ element }));
 			}
 		}
 	}
@@ -209,14 +209,14 @@ class ExtHostTreeView<T> extends Disposable {
 	setSelection(treeItemHandles: TreeItemHandle[]): void {
 		if (!equals(this._selectedHandles, treeItemHandles)) {
 			this._selectedHandles = treeItemHandles;
-			this._onDidChangeSelection.fire({ selection: this.selectedElements });
+			this._onDidChangeSelection.fire(Object.freeze({ selection: this.selectedElements }));
 		}
 	}
 
 	setVisible(visible: boolean): void {
 		if (visible !== this._visible) {
 			this._visible = visible;
-			this._onDidChangeVisibility.fire({ visible: this._visible });
+			this._onDidChangeVisibility.fire(Object.freeze({ visible: this._visible }));
 		}
 	}
 
diff --git a/src/vs/workbench/test/electron-browser/api/extHostTreeViews.test.ts b/src/vs/workbench/test/electron-browser/api/extHostTreeViews.test.ts
index 284f16ac8ee..57894ee26cd 100644
--- a/src/vs/workbench/test/electron-browser/api/extHostTreeViews.test.ts
+++ b/src/vs/workbench/test/electron-browser/api/extHostTreeViews.test.ts
@@ -416,7 +416,7 @@ suite('ExtHostTreeView', function () {
 				assert.deepEqual('treeDataProvider', revealTarget.args[0][0]);
 				assert.deepEqual({ handle: '0/0:a', label: 'a', collapsibleState: TreeItemCollapsibleState.Collapsed }, removeUnsetKeys(revealTarget.args[0][1]));
 				assert.deepEqual([], revealTarget.args[0][2]);
-				assert.equal(void 0, revealTarget.args[0][3]);
+				assert.deepEqual({ select: true, focus: false }, revealTarget.args[0][3]);
 			});
 	});
 
@@ -429,7 +429,7 @@ suite('ExtHostTreeView', function () {
 				assert.deepEqual('treeDataProvider', revealTarget.args[0][0]);
 				assert.deepEqual({ handle: '0/0:a/0:aa', label: 'aa', collapsibleState: TreeItemCollapsibleState.None, parentHandle: '0/0:a' }, removeUnsetKeys(revealTarget.args[0][1]));
 				assert.deepEqual([{ handle: '0/0:a', label: 'a', collapsibleState: TreeItemCollapsibleState.Collapsed }], (<Array<any>>revealTarget.args[0][2]).map(arg => removeUnsetKeys(arg)));
-				assert.equal(void 0, revealTarget.args[0][3]);
+				assert.deepEqual({ select: true, focus: false }, revealTarget.args[0][3]);
 			});
 	});
 
@@ -444,7 +444,7 @@ suite('ExtHostTreeView', function () {
 					assert.deepEqual('treeDataProvider', revealTarget.args[0][0]);
 					assert.deepEqual({ handle: '0/0:a/0:aa', label: 'aa', collapsibleState: TreeItemCollapsibleState.None, parentHandle: '0/0:a' }, removeUnsetKeys(revealTarget.args[0][1]));
 					assert.deepEqual([{ handle: '0/0:a', label: 'a', collapsibleState: TreeItemCollapsibleState.Collapsed }], (<Array<any>>revealTarget.args[0][2]).map(arg => removeUnsetKeys(arg)));
-					assert.equal(void 0, revealTarget.args[0][3]);
+					assert.deepEqual({ select: true, focus: false }, revealTarget.args[0][3]);
 				}));
 	});
 
@@ -458,7 +458,7 @@ suite('ExtHostTreeView', function () {
 		};
 		const revealTarget = sinon.spy(target, '$reveal');
 		const treeView = testObject.createTreeView('treeDataProvider', { treeDataProvider: aCompleteNodeTreeDataProvider() });
-		return treeView.reveal({ key: 'bac' }, { select: false })
+		return treeView.reveal({ key: 'bac' }, { select: false, focus: false })
 			.then(() => {
 				assert.ok(revealTarget.calledOnce);
 				assert.deepEqual('treeDataProvider', revealTarget.args[0][0]);
@@ -467,7 +467,7 @@ suite('ExtHostTreeView', function () {
 					{ handle: '0/0:b', label: 'b', collapsibleState: TreeItemCollapsibleState.Collapsed },
 					{ handle: '0/0:b/0:ba', label: 'ba', collapsibleState: TreeItemCollapsibleState.Collapsed, parentHandle: '0/0:b' }
 				], (<Array<any>>revealTarget.args[0][2]).map(arg => removeUnsetKeys(arg)));
-				assert.deepEqual({ select: false }, revealTarget.args[0][3]);
+				assert.deepEqual({ select: false, focus: false }, revealTarget.args[0][3]);
 			});
 	});
 
@@ -494,7 +494,7 @@ suite('ExtHostTreeView', function () {
 						assert.deepEqual('treeDataProvider', revealTarget.args[0][0]);
 						assert.deepEqual({ handle: '0/0:a/0:ac', label: 'ac', collapsibleState: TreeItemCollapsibleState.None, parentHandle: '0/0:a' }, removeUnsetKeys(revealTarget.args[0][1]));
 						assert.deepEqual([{ handle: '0/0:a', label: 'a', collapsibleState: TreeItemCollapsibleState.Collapsed }], (<Array<any>>revealTarget.args[0][2]).map(arg => removeUnsetKeys(arg)));
-						assert.equal(void 0, revealTarget.args[0][3]);
+						assert.deepEqual({ select: true, focus: false }, revealTarget.args[0][3]);
 					});
 			});
 	});
@@ -533,7 +533,7 @@ suite('ExtHostTreeView', function () {
 						assert.deepEqual('treeDataProvider', revealTarget.args[0][0]);
 						assert.deepEqual({ handle: '0/0:b/0:bc', label: 'bc', collapsibleState: TreeItemCollapsibleState.None, parentHandle: '0/0:b' }, removeUnsetKeys(revealTarget.args[0][1]));
 						assert.deepEqual([{ handle: '0/0:b', label: 'b', collapsibleState: TreeItemCollapsibleState.Collapsed }], (<Array<any>>revealTarget.args[0][2]).map(arg => removeUnsetKeys(arg)));
-						assert.equal(void 0, revealTarget.args[0][3]);
+						assert.deepEqual({ select: true, focus: false }, revealTarget.args[0][3]);
 					});
 			});
 	});