public function root()
    {
        $category = $this->createModel();

        $category = $category->whereExists(function($query)
        {
            $query->select(\DB::raw(1))
                  ->from('category_hierarchy')
                  ->whereRaw(DB::getTablePrefix().'categories.id = '.DB::getTablePrefix().'category_hierarchy.category_id')
                  ->where('category_hierarchy.category_parent_id', 0);
        });

        return $category;
    }