protected function resolveMountPageTree($mountPage)
    {
        $mountPageSourceId = $mountPage['mountPageSource'];
        $mountPageIdentifier = $this->getMountPointIdentifier($mountPage);

        $siteRepository = GeneralUtility::makeInstance(SiteRepository::class);
        /* @var $siteRepository SiteRepository */
        $mountedSite = $siteRepository->getSiteByPageId($mountPageSourceId, $mountPageIdentifier);

        return $mountedSite->getPages($mountPageSourceId);
    }