Porque o SetToolText não funciona

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.tree.*;

/**
 * @author Felipe Lutz
 *
 * To change the template for this generated type comment go to
 * Window>Preferences>Java>Code Generation>Code and Comments
 */
public class Teste_Tree {
	public static void main(String[] args) {
    JFrame frame =new FrameTree();   	
	frame.show();
	}
}

class FrameTree extends JFrame
{
	public FrameTree()
	{
    setTitle("Arvore simples");
    setSize(150,300);
    addWindowListener(new WindowAdapter()
	{ public void WindowClosing(WindowEvent e)
		{
		System.exit(0);
		}
	});
    
    //Configura dados do modelo de arvore
    
    DefaultMutableTreeNode root= new DefaultMutableTreeNode("SUPGS");
	DefaultMutableTreeNode servico= new DefaultMutableTreeNode("PORTAL DE GERENCIA");
	DefaultMutableTreeNode servico2= new DefaultMutableTreeNode("CAS");
	root.add(servico);
	root.add(servico2);
	
	//Mais um teste
	DefaultMutableTreeNode root2= new DefaultMutableTreeNode("SUPCD");
	DefaultMutableTreeNode servico3= new DefaultMutableTreeNode("MAIN FRAME");
	DefaultMutableTreeNode servico4= new DefaultMutableTreeNode("UNIX");
	DefaultMutableTreeNode subservico= new DefaultMutableTreeNode("LINUX");
	servico3.add(subservico);
	root2.add(servico3);
	root2.add(servico4);
		
	//Constroi uma arvore com painel de rolagem
	
	JTree arvore=new JTree(root);
	//arvore.setToolTipText("aa"); ñ funciona!!!!!!!!!!!! aki
	//ToolTipManager.sharedInstance().registerComponent(arvore); nem aki
	Container contentPane=getContentPane();
	contentPane.add(new JScrollPane(arvore));
	
	JTree arvore1=new JTree(root2);
	Container contentPane1=getContentPane();
	contentPane1.add(new JScrollPane(arvore1));
		
	
}