public int getDiameter() {
        if(root == null) return 0;

        int leftHeight = new BinarySearchTreeCode(root.left).getHeight();
        int rightHeight = new BinarySearchTreeCode(root.right).getHeight();

        int leftDiameter = new BinarySearchTreeCode(root.left).getDiameter();
        int rightDiameter = new BinarySearchTreeCode(root.right).getDiameter();

        return Math.max(leftHeight + rightHeight + 1,
                Math.max(leftDiameter, rightDiameter));
    }

    private int getHeight() {
        if(root == null) return 0;
        return Math.max(new BinarySearchTreeCode(root.left).getHeight(),
                new BinarySearchTreeCode(root.right).getHeight())
                + 1;
    }