what event marked the tree loaded complete

[dgz2159]

i had been created a tree like this

tree = new Tree.TreePanel({
el : 'tree-div',
autoScroll : true,
animate : true,
enableDD : true,
rootVisible : false,
containerScroll : true,
loader : new Tree.TreeLoader({
dataUrl : 'viewmdsdata.action' (java server)
})
});

// set the root node
root = new Tree.AsyncTreeNode({
text : 'MDS',
draggable : true,
id : 'source'
});

tree.setRootNode(root);


i want make some default selected node after the tree loaded.
According the API documnet. i try to use

tree.on('load', function(node){
root.firstChild.select();

}

it's not work! and "load" event is called every node added.
Then i try to use "render" event but it won't called
because the AsyncTreeNode has not been expanded.

can any one help,appreciate!