Algorithms and Me: Prune nodes of binary search tree

Given a binary search tree and two integers min and max, prune all nodes of binary search tree which are not in range min and max. 
Key Point: post order traversal
If root is less than min or root is greater than max, we need to remove that node. However there is a catch here. What happens to its child nodes if root node is removed? To take care of this, we need to process children node before processing the root node. 

Node * prune_nodes(Node * root, int min, int max){

        if(root == NULL) return NULL;

        Node * root->left =  prune_node(root->left, min, max);

        Node * root->right = prune_node(root->right, min, max);

        if(root->value < min)

                Node * right_tree = root->right;

                free(root);

                return right_tree;

        }

        if (root->value > max){

                Node *left_tree = root->left;

                free(root);

                return left_tree;

        }

        return root;

}

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