src/vs/base/browser/ui/tree/asyncDataTree.ts/AsyncDataTree/expandOnlyOnTwistieClick
class AsyncDataTree:	get expandOnlyOnTwistieClick(): boolean | ((e: T) => boolean) {
		if (typeof this.tree.expandOnlyOnTwistieClick === 'boolean') {
			return this.tree.expandOnlyOnTwistieClick;
		}

		const fn = this.tree.expandOnlyOnTwistieClick;
		return element => fn(this.nodes.get((element === this.root.element ? null : element) as T) || null);
	}