Draw lines in graphical representation of binary tree

I am trying to draw a binary tree using swing and awt in java. I can already show the nodes of the tree but I am not able to draw the lines of a parent node to its children. I have the node, TreeGUI, DrawTree and Main classes. This image is how the output is without the lines.

My intention is to show rows from a parent node to its child nodes. I tried using method drawLine of Class Graphics but it got like this:

The drawTree method sets the position of the values of the nodes on the screen and saves the position of the nodes in ArrayLists. The drawLine method draws the lines. I believe the rows are that way because the values are saved in that particular order. I've tried several ways and I can't connect the lines correctly. How can I show only one parent's lines to their children?

public class TreeGUI extends JFrame {

    private JPanel contentPane;
    public Node node;
    public DrawTree drawer;

    /**
     * Create the frame.
     */
    public TreeGUI(Node node) {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 500, 500);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        drawer = new DrawTree(node);
        contentPane.add(drawer);
        setContentPane(contentPane);
        this.node = node;
        setVisible(true);
    }

}

class DrawTree extends JPanel{

    public Node node;
    public static ArrayList listX = new ArrayList();
    public static ArrayList listY = new ArrayList();


    public DrawTree(Node node){
        this.node = node;
    }

    @Override
    protected void paintComponent(Graphics g) {
        // TODO Auto-generated method stub
        g.setFont(new Font("Tahoma", Font.BOLD, 20));
        DrawTree(g, 0, getWidth(), 0, getHeight() / node.getheight(node), node);
        listX.clear();
        listY.clear();
    }

    public void DrawTree(Graphics g, int StartWidth, int EndWidth, int StartHeight, int Level, Node node) {
        String data = String.valueOf(node.getValue());
        g.setFont(new Font("Tahoma", Font.BOLD, 20));
        FontMetrics fm = g.getFontMetrics();
        int dataWidth = fm.stringWidth(data);

        g.drawString(data, (StartWidth + EndWidth) / 2 - dataWidth / 2, StartHeight + Level / 2);
        listX.add((StartWidth + EndWidth) / 2 - dataWidth / 2);
        listY.add(StartHeight + Level / 2);
        drawLine(g, node);

        if (node.getLeft() != null) {
            DrawTree(g, StartWidth, (StartWidth + EndWidth) / 2, StartHeight + Level, Level, node.getLeft());
        }
        if (node.getRight() != null)
            DrawTree(g, (StartWidth + EndWidth) / 2, EndWidth, StartHeight + Level, Level, node.getRight());
    }

public void drawLine(Graphics g,  Node node){
       for (int i=1; i < listY.size(); i++)
            g.drawLine((int)listX.get(i-1), (int)listY.get(i-1), (int)listX.get(i), (int)listY.get(i));
    }

}

Main method

public static void main(String[] args) {
    Node raiz = null;
    raiz = raiz.insert(raiz, 35);
    raiz.insert(raiz, 25);
    raiz.insert(raiz, 75);
    raiz.insert(raiz, 30);
    raiz.insert(raiz, 20);
    raiz.insert(raiz, 12);
    raiz.insert(raiz, 6);
    raiz.insert(raiz, 23);
    raiz.insert(raiz, 90);
    TreeGUI gui = new TreeGUI(raiz);
}