protected function _ppBuildTree()
    {
        $aTree = [];
        foreach ($this->_aArray as $oCat) {
            $sParentId = $oCat->oxcategories__oxparentid->value;
            if ($sParentId != 'oxrootid') {
                if (isset($this->_aArray[$sParentId])) {
                    $this->_aArray[$sParentId]->setSubCat($oCat, $oCat->getId());
                }
            } else {
                $aTree[$oCat->getId()] = $oCat;
            }
        }

        $this->assign($aTree);
    }