Delete binary tree

#include<iostream>
using namespace std;

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

void preorder(Node *root){
  if(root==NULL)
     return;
  cout<<" "<<root->data;
  preorder(root->left);
  preorder(root->right);
  }

void DeleteNode(Node * node_ptr){
  if(node_ptr==NULL)
    return;
  DeleteNode(node_ptr->left);
  DeleteNode(node_ptr->right);
  delete node_ptr;
  }

void DeleteTree(Node **root_ref){
 if(*root_ref==NULL)
    return;
 Node *temp=*root_ref;
 DeleteNode(temp);
 *root_ref=NULL;
 }

int main(){
  Node *root=NULL;
  Node *newnode=new Node(1);
  root=newnode;
  root->left=new Node(2);
  root->right=new Node(3);
  (root->left)->left=new Node(4);
  (root->right)->right=new Node(5);
  cout<<"pre order traversal ";
  preorder(root);
  DeleteTree(&root);
  cout<<endl<<"after deletion,pre order traversal is ";
  preorder(root);
  return 0;
  }

 /* DeleteNode ka code ye bhi ho sakta tha.
  void DeleteNode(Node * node_ptr){
    if(node_ptr->left!=NULL)
        DeleteNode(node_ptr->left);
    if(node_ptr->right!=NULL)
        DeleteNode(node_ptr->right);
    delete node_ptr;
    }
*/