template <class _Moveit>
_Nodeptr _Copy_nodes(_Nodeptr _Rootnode, _Nodeptr _Wherenode, _Moveit _Movefl) {
    // copy entire subtree, recursively
    const auto _Scary = _Get_scary();
    _Nodeptr _Newroot = _Scary->_Myhead; // point at nil node

    if (!_Rootnode->_Isnil) { // copy or move a node, then any subtrees
        bool_constant<is_same_v<key_type, value_type>> _Is_set;
        _Nodeptr _Pnode = _Copy_or_move(_Rootnode->_Myval, _Movefl, _Is_set);
        _Pnode->_Parent = _Wherenode;
        _Pnode->_Color  = _Rootnode->_Color;
        if (_Newroot->_Isnil) {
            _Newroot = _Pnode; // memorize new root
        }

        _TRY_BEGIN
        _Pnode->_Left  = _Copy_nodes(_Rootnode->_Left, _Pnode, _Movefl);
        _Pnode->_Right = _Copy_nodes(_Rootnode->_Right, _Pnode, _Movefl);
        _CATCH_ALL
        _Scary->_Erase_tree_and_orphan(_Getal(), _Newroot); // subtree copy failed, bail out
        _RERAISE;
        _CATCH_END
    }

    return _Newroot; // return newly constructed tree
}

if (_Newroot->_Isnil) {
            _Newroot = _Pnode; // memorize new root
}