// import javax.swing.tree.*;
    private DefaultTreeModel m;
    private DefaultMutableTreeNode act;
 
    private void open (String s)
    {
        if (m == null)
        {
            DefaultMutableTreeNode r;
            r = new DefaultMutableTreeNode (s);
            m = new DefaultTreeModel (r);
            jTree1.setModel (m);
            act = r;
        }
        else
        {
            DefaultMutableTreeNode node;
            node = new DefaultMutableTreeNode (s);
            int inx = act.getChildCount();
            m.insertNodeInto (node, act, inx);
            act = node;
        }
    }
 
    private void put (String s)
    {
        DefaultMutableTreeNode node;
        node = new DefaultMutableTreeNode (s);
        int inx = act.getChildCount();
        m.insertNodeInto (node, act, inx);
    }
 
    private void close ()
    {
        if (act != null)
           act = (DefaultMutableTreeNode) act.getParent();
    }

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        open ("Branch");
        put ("item 1");
        put ("item 2");
        open ("Sub Branch");
           put ("sub item");
        close ();
        put ("item 3");
        close ();
    }