here this code when i select product group its show group wise product in filed. but i want to show product group wise without selecting the product group. that means i want to show specific product group product without selection group please help me 

class StockRequisition(models.Model):
    _inherit = 'account.move.line'

    # product_group = fields.Many2one('product.group', string='Product Group')
    # parent_id = fields.Many2one('product.group', string="Product Group")

    @api.onchange('product_group')
    def onchange_product_group(self):
        for rec in self:
            return {'domain': {'product_id': [('product_group', '=', rec.product_group.id)]}}

    product_group = fields.Many2one('product.group', string='Product Group')
    product_id = fields.Many2one('product.product', ondelete='restrict',
                                 string='Consultation Service', help="Consultation Services",
                                 domain=[('hospital_product_type', '=', "consultation")], required=True,
                                 )