source/Application/Model/Category.php
public function isTopCategory()
    {
        if ($this->_blTopCategory == null) {
            $this->_blTopCategory = $this->oxcategories__oxparentid->value == 'oxrootid';
        }

        return $this->_blTopCategory;
    }
public function isTopCategory()
    {
        if ($this->_blTopCategory == null) {
            $this->_blTopCategory = $this->oxcategories__oxparentid->value == 'oxrootid';
        }

        return $this->_blTopCategory;
    }
public function isTopCategory ( ) { if ( $ this -> _blTopCategory == null ) { $ this -> _blTopCategory = $ this -> oxcategories__oxparentid -> value == 'oxrootid' ; } return $ this -> _blTopCategory ; }
Returns true if category parentid is 'oxrootid'

@return bool
Returns true if category parentid is oxrootid