Function inside the constructors are not working Any Help

For example my constructor is given below and the following is not working if it is in the constructor . But it works outside the constructor

PHP Code:

public function _construct()
{
    $this->session = \Config\Services::session();
    $menu = new MenuModel();  
    $data['menu_list'] = $menu->get_menu_list(session()->role_id);   
    echo view('common/menu',$data);
}