How to expand tree in gwt?

I a using GWT 2.3.In which I am using import com.google.gwt.user.client.ui.Tree. I want to show tree expanded always.For that I did below code for every tree item

    treeItem.setState(true);

But it is not working.I am not getting how to expand tree. Please help me out.Thanks in advance

Do you expand the tree before you add child items to it? In that case he doesn't get expanded.

Here is an example which works for me:

private Tree createTree() {
    // Create a Tree
    TreeItem root = new TreeItem("root");
    root.addItem("item0");
    root.addItem("item1");
    root.addItem("item2");

    TreeItem childwithsubchilder = new TreeItem("subitmes");
    childwithsubchilder.addItem("item0");
    childwithsubchilder.addItem("item1");
    childwithsubchilder.addItem("item2");

    root.addItem(childwithsubchilder);

    // expand the element
    root.setState(true);

    Tree t = new Tree();
    t.addItem(root);
    return t;
}