With MyGWT, to add a child to a tree, i had only to do model.add(child).
But with GXT, it seems that's don't work.
The "child" TreeItem is never showed.
What's wrong with my code ?

public class Test implements EntryPoint {

   * This is the entry point method.
  public void onModuleLoad() {

    Tree tree = new Tree();
    BaseTreeLoader loader = new BaseTreeLoader(new TreeModelReader());
    TreeStore<Model> store = new TreeStore<Model>(loader);
    TreeBinder<Model> binder = new TreeBinder<Model>(tree, store);
    store.setModelComparer(new DefaultModelComparer<Model>());
    Window window = new Window();
    window.setLayout(new FitLayout());
    BaseTreeModel root = new BaseTreeModel();
    root.set("name", "ROOT");
    // add the root
    store.add(root, true);
    BaseTreeModel child = new BaseTreeModel();
    // add one child
    child.set("name", "CHILD");
    store.add(root, child, true);
    // only one node is show
    // "child" is not added to the Tree