Write a program in C++ to find post-order predecessor of a node in a Binary Tree

#include <iostream>
using namespace std;
struct Node {
   struct Node *left, *right, *parent;
   int value;
};
struct Node* insertNode(int value) {
   Node* temp = new Node;
   temp->left = temp->right = temp->parent = NULL;
   temp->value = value;
   return temp;
}
Node* findPostorderSuccessor(Node* root, Node* n) {
   if (n == root)
      return NULL;
   Node* parent = n->parent;
   if (parent->right == NULL || parent->right == n)
      return parent;
   Node* curr = parent->right;
   while (curr->left != NULL)
      curr = curr->left;
   return curr;
}
int main(){
   struct Node* root = insertNode(6);
   root->parent = NULL;
   root->left = insertNode(2);
   root->left->parent = root;
   root->left->left = insertNode(8);
   root->left->left->parent = root->left;
   root->left->right = insertNode(4);
   root->left->right->parent = root->left;
   root->right = insertNode(9);
   root->right->parent = root;
   root->right->left = insertNode(7);
   root->right->left->parent = root->right;
   root->left->right->left = insertNode(14);
   struct Node* successorNode = findPostorderSuccessor(root, root->left->right);
   if (successorNode)
      cout<<"Postorder successor of "<<root->left->right->value<<" is "<<successorNode->value;
   else
      cout<<"Postorder successor of "<<root->left->right->value<<" is NULL";
   return 0;
}