The tree package contains classes that allow you to build up visual    trees, like the ones you are familiar with e.g. for browsing your file    system. Expanding    and collapsing tree nodes is handled automatically by showing or hiding the    contained subtree structure.       To construct a tree, start up with the {@link qx.ui.tree.Tree Tree} class,    then use {@link qx.ui.tree.TreeFolder TreeFolder} and {@link    qx.ui.tree.TreeFile TreeFile} objects to populate your tree.       Example       Here is a little example of how to use the widget.       <pre class='javascript'>     Create the tree widget    var tree = new qx.ui.tree.Tree().set({      width : 200,      height : 400    });         Create a folder and set it the root folder    var root = new qx.ui.tree.TreeFolder("root");    tree.setRoot(root);         Create some folders:    var te1_1 = new qx.ui.tree.TreeFolder("Files");    var te1_2 = new qx.ui.tree.TreeFolder("Workspace");    var te1_3 = new qx.ui.tree.TreeFolder("Network");    var te1_4 = new qx.ui.tree.TreeFolder("Trash");        Create some content (leaves) and add it to the "Files" folder:    var te1_2_1 = new qx.ui.tree.TreeFile("Windows (C:)");    var te1_2_2 = new qx.ui.tree.TreeFile("Documents (D:)");    te1_2.add(te1_2_1, te1_2_2);         Add the content to the root folder    root.add(te1_1, te1_2, te1_3, te1_4);         Add the root widget to the application    this.getRoot().add(tree);    <pre>       This example creates a tree with four folders inside it's root folder.        External Documentation       <a href='http:manual.qooxdoo.org${qxversion}pageswidgettree.html' target='_blank'>    Documentation of this widget in the qooxdoo manual.<a>