public void insert(int id, double data) {
        Node current = root;
        while (true) {
            if (id < current.id) {
                if (current.leftChild == null) {
                    current.leftChild = new Node(id, data);
                    break;
                } else {
                    current = current.leftChild;
                }
            } else {
                if (current.rightChild == null) {
                    current.rightChild = new Node(id, data);
                    break;
                } else {
                    current = current.rightChild;
                }
            }
        }
    }