java 动态的给树添加新节点 望高手指点啊

//先选中节点才能增加节点
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.tree.*;

public class TreeTest implements ActionListener,TreeModelListener{
JLabel label=null;
JTree tree=null;
DefaultTreeModel treeModel=null;
String nodeName=null;//原有节点名称

public TreeTest(){
JFrame f=new JFrame("TreeTest");
Container contentPane=f.getContentPane();

DefaultMutableTreeNode root=new DefaultMutableTreeNode("资源管理器");

tree=new JTree(root);
tree.setEditable(true);
tree.addMouseListener(new MouseHandle());
treeModel=(DefaultTreeModel)tree.getModel();
treeModel.addTreeModelListener(this);

JScrollPane scrollPane=new JScrollPane();
scrollPane.setViewportView(tree);

JPanel panel=new JPanel();
JButton b=new