//instantiate the TreeView control:
var tree = new YAHOO.widget.TreeView("treeDiv1");

//get a reference to the root node; all
//top level nodes are children of the root node:
var rootNode = tree.getRoot();

//begin adding children
var tmpNode = new YAHOO.widget.TextNode("My nodelabel", tree.getRoot(), false);

//the tree won't show up until you draw (render) it:
tree.draw();

//Add a window onload handler to build the tree when the load 
//event fires. 
YAHOO.util.Event.addListener(window, "load", treeInit);