when i select regulation from dropdown to auto populate the data into tree view. small vague with this please help me

this is my py file:

class studentreg(models.Model):
    _name='student.registration'
    _description='Student registration'

     regulation=fields.Selection([('r10','R10'),('r16','R16')],required=True)
    supply_data=fields.One2many('page.studentregistration','failed_data')

@api.multi
    @api.onchange('regulation')
    def onchange_get_faileddata(self):
       
        stud_list = []
        stud_obj = self.env['faileddata.form']
        for rec in self:
            if rec.regulation:
                stud_list = [{'subject_code': stu.sub_code,'subject_name': stu.sub_name,'subject_type':stu.sub_type}
                             for stu in stud_obj.search([('regulation', '=',
                                                          rec.regulation.id),

                                                         ])]
            rec.supply_data = stud_list

class faileddataform(models.Model):
    _name='faileddata.form'
    _description='failed data'
   

    sub_code = fields.Char('Subject Code')
    sub_name = fields.Char('Subject Name')
    sub_type = fields.Char('Subject Type')