level having maximum sum in a binary tree

#include<iostream>
#include<queue>
using namespace std;

class Node{
  public:
      int data;
      Node *left,*right;
      Node(int key){
        data=key;
        left=NULL;
        right=NULL;
        }
  };

int MaximumSumLevel(Node *root){
if(root==NULL)
   return 0;
queue<Node*>q;
int max_sum=INT_MIN,curr_sum=0,max_sum_level=0,curr_level=0;
q.push(root);
q.push(NULL);
while(!q.empty()){
  Node *temp=q.front();
  q.pop();
  if(temp!=NULL){
     curr_sum=curr_sum+temp->data;
    if(temp->left!=NULL)
        q.push(temp->left);
    if(temp->right!=NULL)
        q.push(temp->right);
    }
   else{
        curr_level++;
        if(max_sum<curr_sum){
            max_sum=curr_sum;
            max_sum_level=curr_level;
            }
        curr_sum=0;
        if(q.size()>0)
          q.push(NULL);
    }
   }
   cout<<"maximum sum is "<<max_sum;
return max_sum_level;
  }

int main(){
  Node *root1=NULL;
  Node *newnode=new Node(1);
  root1=newnode;
  root1->left=new Node(2);
  root1->right=new Node(3);
  (root1->left)->left=new Node(4);
  (root1->right)->right=new Node(5);
  ((root1->left)->left)->left=new Node(6);
  cout<<endl<<"level is "<<MaximumSumLevel(root1);
  return 0;
  }