Tree Painter assignment - step 1

package treePainter;

import java.awt.EventQueue;
import java.awt.Graphics;

import javax.swing.JFrame;
import java.awt.Toolkit;
import javax.swing.JButton;
import java.awt.BorderLayout;
import javax.swing.JPanel;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.UIManager;

public class Main {

    private JFrame frmTreePainter;
    private JTextField textField;

    class MyPanel extends JPanel {
        private static final long serialVersionUID = 1L;
        int levels = 4;

        void paintTree(Graphics g, int x, int y, int level) {
            if (level < levels) {
                g.drawOval(x, y, 10, 10);
                g.drawString(""+x, x, y);
                int distance=30;
                paintTree(g, x - distance, y + 20, level + 1);
                paintTree(g, x + distance, y + 20, level + 1);
                if (level < levels-1) {
                    g.drawLine(x, y, x+distance, y+20);
                    g.drawLine(x, y, x-distance, y+20);
                }

            }
        }

        @Override
        public void paint(Graphics g) {
            // TODO Auto-generated method stub
            super.paint(g);
            paintTree(g, frmTreePainter.getWidth()/2, 10, 0);
        }

    }

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsClassicLookAndFeel");
        } catch (Throwable e) {
            e.printStackTrace();
        }
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Main window = new Main();
                    window.frmTreePainter.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public Main() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frmTreePainter = new JFrame();
        frmTreePainter.setTitle("Tree Painter");
        frmTreePainter.setIconImage(Toolkit.getDefaultToolkit()
                .getImage(Main.class.getResource("/javax/swing/plaf/metal/icons/sortUp.png")));
        frmTreePainter.setBounds(100, 100, 450, 300);
        frmTreePainter.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panelForControls = new JPanel();
        frmTreePainter.getContentPane().add(panelForControls, BorderLayout.NORTH);

        JLabel lblNewLabel = new JLabel("Tree levels:");
        panelForControls.add(lblNewLabel);

        textField = new JTextField();
        textField.setText("4");
        panelForControls.add(textField);
        textField.setColumns(10);

        JButton btnDrawIt = new JButton("Draw it!");
        panelForControls.add(btnDrawIt);

        MyPanel panel = new MyPanel();
        frmTreePainter.getContentPane().add(panel, BorderLayout.CENTER);
    }

}