Method getCategoryChildrenArray

public static function getCategoryChildrenArray($id)
{
    $db = Factory::getDBO();
    $query = "SELECT id FROM #__phocacart_categories WHERE parent_id = " . (int) $id;
    $db->setQuery($query);
    $categories = $db->loadColumn();
    $children = array();
    if (!empty($categories)) {
        foreach ($categories as $k => $v) {
            $children[$v] = self::getCategoryChildrenArray($v);
        }
    }
    return $children;
}