How add to realtion data from other table?

I want add subquery to my model in laravel. I have order model with standard class and i can take all model columns using:

$order = Order::find(3); 

But i need add method to class order like CHECKLIST. This checklist is the same for any order like:

SELECT o.*, (SELECT * FROM checklist) FROM order o WHERE o.id = 3

Is any way to add this subquery as method in class ?

namespace App;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;

class Order extends Model
{
    use SoftDeletes;
    public function checklist() {
        return 
    }                
}

via Chebli Mohamed