deleting leaves the weird way

void delete_leaf(BSTNode *tnode)
{
    //deletes the leaf node tnode from the BST - works
    BSTNode *ptr, *pre_ptr;

    ptr = root;
    pre_ptr = root; //pre_ptr is the parent of the root


    while (ptr -> data != tnode -> data)
    {
        pre_ptr = ptr;
        printf("\ntnode -> data = %d, ptr -> data =%d\n", tnode -> data, ptr -> data);
        if (ptr -> data < tnode -> data)
        {
            printf("\ntaking left");
            ptr = ptr -> left;
        }

        else
        {
            printf("\ntaking right");
            ptr = ptr -> right;
        }
    }

    free(ptr);

    pre_ptr -> right = NULL;
    pre_ptr -> left = NULL;

    //print_ascii_tree(root);

}