src/vs/base/browser/ui/tree/indexTreeModel.ts/IndexTreeModel/setCollapsed
class IndexTreeModel:	setCollapsed(location: number[], collapsed?: boolean, recursive?: boolean): boolean {
		const node = this.getTreeNode(location);

		if (typeof collapsed === 'undefined') {
			collapsed = !node.collapsed;
		}

		const update: CollapsedStateUpdate = { collapsed, recursive: recursive || false };
		return this.eventBufferer.bufferEvents(() => this._setCollapseState(location, update));
	}