* @param {Function} callback (optional) A callback to be called when\r
* expanding this node completes (does not wait for deep expand to complete).\r
* Called with 1 parameter, this node.\r
* @param {Function} callback (optional) A callback to be called when\r
* expanding this node completes (does not wait for deep expand to complete).\r
* Called with 1 parameter, this node.\r