private void init()
  {
    contentDiv = DOM.createDiv();
    setElement( contentDiv );
    contentDiv.setClassName( NavigationTreeResources.INSTANCE.css().mainContainer() );
    listElement = DOM.createElement( "ul" );
    DOM.appendChild( contentDiv, listElement );
    Event.sinkEvents( listElement, Event.ONCLICK );
    Event.setEventListener( listElement, this );
  }