Refferal program in Eloquent : Self referencing table with pivot one to many

For a referral program I have two tables. users (with an id and some other columns) and referrals (with a referrer_id and a referred_id).

A User may have many referred users, and User may have only one referrer User. So User model should be like:

class User extends Model 
{

    public function referrerUser()
    {
        // There may be only one referrer user for this user
    }

    public function referredUsers()
    {
        // There may be many referred users for this user
    }
}

I read some messages about this, but I'm a bit confused about the right way to do this. So, how can I return these relations using belongsTo (for referrerUser method) and belongsToMany (for referredUsers method)?

via Chebli Mohamed