function insertLazyTreeChildAt(parentNode, childTree, referenceNode) {
	  DOMLazyTree.insertTreeBefore(parentNode, childTree, referenceNode);
	}
Inserts `childNode` as a child of `parentNode` at the `index`.

@param {DOMElement} parentNode Parent node in which to insert.
@param {DOMElement} childNode Child node to insert.
@param {number} index Index at which to insert the child.
@internal