Thread: Jtree help

I have a problem with my Jtree.....I can add nodes to my JTree, but after expanding a node, I can not add any child nodes to that node

import java.util.*;
import javax.swing.*;
import java.awt.*;
import javax.swing.event.*;
import java.awt.event.*;
import javax.swing.tree.*;
import java.awt.Color;
public class GUIMP extends JFrame implements ActionListener {
	String Sname="";
	String Semail="";
	int iConNum=0;
	int id=0;
//icons& images
ImageIcon mid;
ImageIcon image;
ImageIcon del;
ImageIcon edi;
ImageIcon exi;
ImageIcon cle;
ImageIcon bg1;
JLabel bgd;
ImageIcon bg2;
JLabel bgd2;
JLabel git;
//components
JPanel panel1=new JPanel();
JPanel panel2= new JPanel();
JFrame frame2=new JFrame();
JButton Add;
JButton Delete;
JButton Edit;
JButton Exit;
JButton Clear;
JLabel label;
JTextField name;
JLabel label2;
JTextField email;
JLabel label3;
JTextField ConNum;
//Components for frame 2
JLabel lab;
JTextField nam;
JLabel lab2;
JTextField ema;
JLabel lab3;
JTextField num;
JButton sub;
JButton can;
//Jtree
JTree tree ;
DefaultMutableTreeNode parent;   
 
    public GUIMP() {
    	//settings
    	//frame2
    	 frame2.setTitle("Adding Info");
    	 frame2.setLocation(325,350);
         frame2.setSize(372, 144);
         //main frame
    	 setTitle("Phonebook Tree");
    	 setLocation(250,200);
         setSize(500,446);
         setDefaultCloseOperation(3);
         setLayout(null);
         frame2.setLayout(null);
         panel1.setLayout(null);
         panel2.setLayout(null);
         panel2.setSize(500,400);
 
          //splitpane
         JSplitPane splitPane = new JSplitPane( JSplitPane.HORIZONTAL_SPLIT, panel1,panel2 ); 
         splitPane.setResizeWeight(0.5);
         splitPane.setContinuousLayout(true);
         splitPane.setOneTouchExpandable(true);
         splitPane.setBounds(0,0,500,1000);
         add(splitPane);
 
         //Buttons
        image=new ImageIcon("add.jpg");
        Add=new JButton(image);
        Add.setBounds(5,5,45,50);
        panel1.add(Add);
        Add.addActionListener(this);
 
        del=new ImageIcon("delete.png");
        Delete=new JButton(del);
        Delete.setBounds(80,5,45,50);
        panel1.add(Delete);
        Delete.addActionListener(this);
 
        edi=new ImageIcon("edit.jpg");
        Edit=new JButton(edi);
        Edit.setBounds(160,5,45,50);
        panel1.add(Edit);
        Edit.addActionListener(this);
 
        cle=new ImageIcon("clear.png");
        Clear=new JButton(cle);
        Clear.setBounds(0,370,65,35);
        panel2.add(Clear);
        Clear.addActionListener(this);
 
        exi=new ImageIcon("exit.gif");
        Exit=new JButton(exi);
        Exit.setBounds(150,370,85,35);
        panel2.add(Exit);
        Exit.addActionListener(this);
 
        //Buttons for Frame 2
        sub=new JButton("Submit");
        sub.setBounds(265,25,100,25);
        sub.addActionListener(this);
        frame2.add(sub);
 
        can=new JButton("Cancel");
        can.setBounds(265,75,100,25);
        can.addActionListener(this);
        frame2.add(can);
 
        //Jtree
        parent= new DefaultMutableTreeNode("Digital Phonbook Contacts", true);
        tree= new JTree(parent);
 
        tree.setBounds(0,80,400,200);
        //------------makes Jtree transparent---------------
        //code snippet from [url=http://java.itags.org/java-core-gui-apis/40693/]Java Core GUI APIs: How to make JTree transparent? - java.itags.org[/url]
        tree.setOpaque(false);
        tree.setCellRenderer(new DefaultTreeCellRenderer(){
        public Component getTreeCellRendererComponent(JTree tree,Object value,
        boolean sel,boolean expanded,boolean leaf,int row,boolean hasFocus){
        super.getTreeCellRendererComponent(tree,value,sel,expanded,leaf,row,hasFocus);
        this.setBackgroundSelectionColor(null);
        this.setBorderSelectionColor(null);
        this.setBackgroundNonSelectionColor(new Color(0,0,0,0));
        return this;
         }
          });
        //-------------------------------------------------
        panel1.add(tree);
 
 
 
         //TextFields and Labels
         label=new JLabel("Name: ");
         label.setForeground(Color.white);
         label.setBounds(50,5,100,25);
         panel2.add(label);
 
         name=new JTextField();
          name.setBackground(Color.YELLOW);
         name.setBounds(105,10,100,25);
         panel2.add(name);
         name.setEditable(false);
 
         label2=new JLabel("Email:");
         label2.setForeground(Color.white);
         label2.setBounds(50,50,100,25);
         panel2.add(label2);
 
         email=new JTextField();
         email.setBounds(105,50,100,25);
         email.setBackground(Color.YELLOW);
         panel2.add(email);
         email.setEditable(false);
 
         label3=new JLabel("Contact Number:");
         label3.setForeground(Color.white);
         label3.setBounds(5,85,100,25);
         panel2.add(label3);
 
         ConNum=new JTextField();
         ConNum.setBackground(Color.YELLOW);
         ConNum.setBounds(105,85,100,25);
         ConNum.setEditable(false);
         panel2.add(ConNum);
 
         //background
         bg1=new ImageIcon("night.jpg");
         bgd=new JLabel(bg1);
         bgd.setBounds(0,0,257,410);
         panel1.add(bgd);
 
         bg2=new ImageIcon("day.jpg");
         bgd2=new JLabel(bg2);
         bgd2.setBounds(0,0,257,411);
         panel2.add(bgd2);
 
 
 
 
         //Textfields and labels for frame 2
         lab=new JLabel("Name:");
         lab.setBounds (55, 5, 100, 25);
         frame2.add(lab);
 
         nam=new JTextField();
         nam.setBounds (110, 10, 100, 25);
         frame2.add(nam);
 
         lab2=new JLabel("Email:");
         lab2.setBounds (55, 45, 100, 25);
         frame2.add(lab2);
 
         ema=new JTextField();
         ema.setBounds (110, 45, 100, 25);
         frame2.add(ema);
 
         lab3=new JLabel("Contact Number:");
         lab3.setBounds (5, 80, 100, 25);
         frame2.add(lab3);
 
         num= new JTextField();
         num.setBounds (110, 80, 100, 25);
         frame2.add(num);
 
         mid=new ImageIcon("mid.jpg");
         git=new JLabel(mid);
         git.setBounds(0,0,590,189);
         frame2.add(git);
 
 
 
 
 
         //----------------------------
         setVisible(true);
 
 
 
 
    }
 
 
    public void actionPerformed(ActionEvent a)
    	{
    		if(a.getSource()==can){
    			frame2.setVisible(false);
    		}
    		if(a.getSource()==Delete){
 
 
    		}
    		if(a.getSource()==Add){
    			frame2.setVisible(true);
    		}
 
    		if(a.getSource()==Exit){
			dispose();
		}
 
			if(a.getSource()==sub){
		Sname=nam.getText();
        Semail=ema.getText();
        try
        {
            iConNum=Integer.parseInt(""+num.getText());
        }
        catch(Exception e)
        {
            JOptionPane.showMessageDialog(null, "Please enter Phone Number");
        }
        if(Sname.equals(""))
        {
            JOptionPane.showMessageDialog(null, "Please Enter Name");
        }
        else
        {
         Contact person=new Contact(Sname, Semail, iConNum);
         Vector<String> bla=new Vector<String>();
         DefaultMutableTreeNode category = null;
         category = new DefaultMutableTreeNode("Contact"+Contact.getID());
         JOptionPane.showMessageDialog(null, "Person Saved");
         parent.add(category);
         DefaultMutableTreeNode name= new DefaultMutableTreeNode(nam.getText());
         DefaultMutableTreeNode email = new DefaultMutableTreeNode(ema.getText());
         DefaultMutableTreeNode number = new DefaultMutableTreeNode(num.getText());
         category.add(name);
         category.add(email);
         category.add(number);
    }
 
			}
 
 
    	}
 
     public static void main(String[]args)
        {
            GUIMP var=new GUIMP();
            var.setVisible(true);
 
    }
 
 
}

Please Help..Thank You!