One table or the other

SELECT *
  FROM (
       SELECT `id` AS t1id,
              `name` AS t1name,
              `parentGroup` AS t1parent
         FROM `usergroup`
        WHERE `vhost` = 975 AND
              `treeleft` BETWEEN (SELECT `treeleft`
                                    FROM `usergroup`
                                   WHERE `vhost` = 975 AND
                                         `id` = 40139) AND
                         (SELECT `treeright`
                                    FROM `usergroup`
                       WHERE `vhost` = 975 AND
                         `id` = 40139) AND
             (`treeright` - `treeleft`) = 1) AS t1
INNER JOIN
     (   SELECT `id` AS t2id,
        `name` AS t2name
           FROM `usergroup`
          WHERE `vhost` = 975 AND
                `parentGroup` = 40139
     ) AS t2 ON t2id = t1parent