src/vs/workbench/api/common/extHostTreeViews.ts/ExtHostTreeView/addNodeToParentCache
class ExtHostTreeView:	private addNodeToParentCache(node: TreeNode, parentNode: TreeNode | Root): void {
		if (parentNode) {
			if (!parentNode.children) {
				parentNode.children = [];
			}
			parentNode.children.push(node);
		} else {
			if (!this.roots) {
				this.roots = [];
			}
			this.roots.push(node);
		}
	}