Laravel Many to Many on same Model

users
 - id
 - type (string)

user_user
 - user_id_1
 - user_id_2
 
User extends Model {
  ....
    public function agents()
    {
        return $this->belongsToMany(
            User::class,
            'user_user',
            'user_id_1',
            'user_id_2')
            ->where('type', '=', 'agent');
    }
    // and so on
    .... 
}

// Then I can save it with
$agent = factory(User::class)->create(['type' => 'agent']);
User::agents()->save($agent);

// And output it with
return User::agents(); // Collection of users with agent type