CI_Session::set_userdata PHP Method

    public function set_userdata($data, $value = NULL)
    {
        if (is_array($data)) {
            foreach ($data as $key => &$value) {
                $_SESSION[$key] = $value;
            }
            return;
        }
        $_SESSION[$data] = $value;
    }

 /**
  * Setea el menu
  */
 public function setCollapse()
 {
     $menu_collapse = $this->session->userdata("menu_collapse");
     if ($menu_collapse) {
         $this->session->set_userdata("menu_collapse", false);
     } else {
         $this->session->set_userdata("menu_collapse", true);
     }
 }