code: private void fireTreeStructureChanged()
     {
        // Guaranteed to return a non-null array
        Object[] listeners = m_listenerList.getListenerList();
        TreeModelEvent e = null;
        // Process the listeners last to first, notifying
        // those that are interested in this event
        for (int i = listeners.length - 2; i >= 0; i -= 2)
        {
           if (listeners[i] == TreeModelListener.class)
           {
              // Lazily create the event:
              if (e == null)
              {
                 e = new TreeModelEvent(getRoot(), new Object[]
                 {
                    getRoot()
                 }, null, null);
              }
              ((TreeModelListener) listeners[i + 1]).treeStructureChanged(e);
           }
        }
     }
docs: Notify listeners that the tree structure has changed.