Add 1 to a Linked List Number

class Solution {
    public Node addOne(Node head) {
        // code here.
        int carry = helper(head);
        if(carry > 0){
            Node node = new Node(1);
            node.next = head;
            head = node;
        }
        return head;
    }
    
    private int helper(Node node){
        if(node == null) return 1;
        int carry = helper(node.next);
        node.data = node.data+carry;
        if(node.data > 9){
            node.data = 0;
            return 1;
        }
        return 0;
    }
}