CodeIgniter Cart Extend for insert to add

MY_Cart.php

class MY_Cart extends CI_Cart {
    private function _is_identical($a, $b) {
        sort($a);
        sort($b);

        return $a == $b;
    }

    public function insert($data) {
        foreach ($this->contents() as $item) {
            if ($item['id']==$data['id'] && $this->_is_identical($item['options'],$data['options'])) {
                $update_data = array(
                    'rowid' => $item['rowid'],
                    'qty'   => ($item['qty']+1)
                );
                $this->update($update_data);
                return $item['rowid'];
            }
        }
        return parent::insert($data);
    }
}