src/vs/workbench/api/common/extHostTreeViews.ts/ExtHostTreeView/clearChildren
class ExtHostTreeView:	private clearChildren(parentElement?: T): void {
		if (parentElement) {
			const node = this.nodes.get(parentElement);
			if (node) {
				if (node.children) {
					for (const child of node.children) {
						const childElement = this.elements.get(child.item.handle);
						if (childElement) {
							this.clear(childElement);
						}
					}
				}
				node.children = undefined;
			}
		} else {
			this.clearAll();
		}
	}