(1)
var store = App.TreePanel1.getStore(),
node = store.getNodeById("Node1");
node.appendChild({
text : "The New Node",
leaf : true
})
(2)
var sm = App.TreePanel1.getSelectionModel();
selectedNode,
parentNode;
if (sm.hasSelection()) {
selectedNode = sm.getSelection()[0],
parentNode = selectedNode.parentNode;
}