How to use org.apache.wicket.extensions.markup.html.tree

@Override
protected void onNodeLinkClicked(Object node, BaseTree tree, AjaxRequestTarget target)
{
  super.onNodeLinkClicked(node, tree, target);
  LinkTree.this.onNodeLinkClicked(node, tree, target);
}

  @Override
  public void onClick(final AjaxRequestTarget target)
  {
    getTreeState().selectNode(node, !getTreeState().isNodeSelected(node));
    onNodeLinkClicked(target, node);
    if (target != null)
    {
      updateTree(target);
    }
  }
});

protected String getItemClass(Object node)
{
  if (getTreeState().isNodeSelected(node))
  {
    return getSelectedClass();
  }
  else
  {
    return null;
  }
}

/**
 * Initialize the component.
 */
private void init()
{
  setVersioned(false);
  // we need id when we are replacing the whole tree
  setOutputMarkupId(true);
  // create container for tree items
  itemContainer = new TreeItemContainer("i");
  add(itemContainer);
  checkModel();
}

/**
 * Tree constructor.
 * 
 * @param id
 *            The component id
 * @param model
 *            The tree model
 */
public DefaultAbstractTree(final String id, final TreeModel model)
{
  super(id, new WicketTreeModel());
  setModelObject(model);
}

  private boolean hasParentWithChildrenMarkedToRecreation()
  {
    return getParentItem() != null &&
      (getParentItem().getChildren() == null || getParentItem().hasParentWithChildrenMarkedToRecreation());
  }
}

@Override
public final void nodeUnselected(Object node)
{
  if (isNodeVisible(node))
  {
    invalidateNode(node, isForceRebuildOnSelectionChange());
  }
}

  @Override
  protected Component newContentComponent(String componentId, BaseTree tree,
    IModel<?> model)
  {
    return super.newContentComponent(componentId, tree, getNodeTextModel(model));
  }
};

/**
 * Construct.
 * 
 * @param id
 * @param model
 *            Tree model
 */
public LabelTree(String id, TreeModel model)
{
  super(id, new WicketTreeModel());
  setModelObject(model);
}

/**
 * @see Component#getMarkupId()
 */
@Override
public String getMarkupId()
{
  // this is overridden to produce id that begins with id of tree
  // if the tree has set (shorter) id in markup, we can use it to
  // shorten the id of individual TreeItems
  return AbstractTree.this.getMarkupId() + "_" + getId();
}

/**
 * Call the callback#visitItem method for the given item and all it's children.
 * 
 * @param item
 *            The tree item
 * @param callback
 *            item call back
 */
private void visitItemAndChildren(TreeItem item, IItemCallback callback)
{
  callback.visitItem(item);
  visitItemChildren(item, callback);
}

  @Override
  public String getObject()
  {
    return renderNode(node);
  }
}));

/**
 * 
 * Construct.
 * 
 * @param id
 * @param model
 *            Tree model
 */
public LinkTree(String id, TreeModel model)
{
  super(id, new WicketTreeModel());
  setModelObject(model);
}

  /**
   * @see org.apache.wicket.markup.html.link.Link#onClick()
   */
  @Override
  public void onClick()
  {
    callback.onClick(null);
  }
};

@Override
public final void nodeCollapsed(Object node)
{
  if (isNodeVisible(node) == true)
  {
    invalidateNodeWithChildren(node);
  }
}

  @Override
  public void visitItem(TreeItem item)
  {
    // render component
    item.render();
  }
};

/** called when all nodes are collapsed. */
@Override
public final void allNodesCollapsed()
{
  invalidateAll();
}

  @Override
  public void visitItem(TreeItem item)
  {
    item.detach();
  }
});

  @Override
  public void visitItem(TreeItem item)
  {
    item.beforeRender();
  }
});

/**
 * Tree constructor
 * 
 * @param id
 *            The component id
 */
public AbstractTree(String id)
{
  super(id);
  init();
}