Given a Binary Tree, write a function to check whether the given Binary Tree is a prefect Binary Tree or not. A Binary tree is Perfect Binary Tree in which all internal nodes have two children and all leaves are at same level.

Example 1:

Input: 
          7
      /  \
     4    9
Output: YES
Explanation: 
As the root node 7 has two children and 
two leaf nodes 4 and 9 are at same level 
so it is a perfect binary tree.

Example 2:

Input: 
                   7
              /   \
             3     8
           /   \     \
          2     5     10
        /
       1
Output: NO

Your task:

You don't need to read input or print anything. Your task is to complete the function isPerfect() which takes root node of the tree as input parameter and returns a boolean value.If the tree is a perfect binary tree return true other wise return false.

Expected Time Complexity: O(N)
Expected Auxiliary Space: O(N)

Constraints:
1<=T<=10^5
1<=N<=10^5
1<=data of node<=10^5