Laravel parent / child relationship on its own model

I would like to receive all vouchers that have at least one child, a voucher can have multiple voucher children, but any voucher can only have one parent.

I have set it up with the following models and calls, and the request it generates as desired, for now this part: 'vouchers'.'parent_id' = 'vouchers'.'id'

Required functionality:

$vouchers = Voucher::has('children')->get();

      

        
        
        
      

    

or

$vouchers = Voucher::has('parent')->get();

      

        
        
        
      

    

Result Query

select * from `vouchers` where `vouchers`.`deleted_at` is null 
and (select count(*) from `vouchers` where `vouchers`.`deleted_at` is null 
and `vouchers`.`parent_id` = `vouchers`.`id` 
and `vouchers`.`deleted_at` is null ) >= 1

      

        
        
        
      

    

Model:

class Voucher extends baseModel {

    public function parent()
    {
        return $this->belongsTo('Voucher', 'parent_id');
        // return $this->belongsTo('Voucher', 'parent_id', 'id'); <- attempted but din't work
    }

    public function children()
    {
        return $this->hasMany('Voucher', 'parent_id');
    }
}