class Tree extends Composite implements HasSelectionHandlers<T>,
                                                                   HasOpenHandlers<T>,
                                                                   HasCloseHandlers<T> {

    @SuppressWarnings("unchecked")
    public T addItem(final T item) {
        container.add(item);
        item.setTree(this);
        return item;
    }

    public  Tree();
      Tree(final Supplier<FlowPanel> containerProvider);

}