Double the tree such that insert new duplicate node for each node using cpp

/\*  
 For each node in a binary search tree,  
 create a new duplicate node, and insert  
 the duplicate as the left child of the original node.  
 The resulting tree should still be a binary search tree.  So the tree...  
 2  
 / \\  
 1   3  
 Is changed to...  
 2  
 / \\  
 2   3  
 /   /  
 1   3  
 /  
 1  
\*/  
void doubleTree(struct node\* node) {  
  struct node\* oldLeft;  
  if (node==NULL) return;  
  // do the subtrees  
  doubleTree(node->left);  
  doubleTree(node->right);  
  // duplicate this node to its left  
  oldLeft = node->left;  
  node->left = newNode(node->data);  
  node->left->left = oldLeft;  
}