问不支持EF6嵌套事务

EN

using (MaintenanceDB db = new MaintenanceDB())
        {
            try
            {
                employee employee = new employee
                {
                    ID = idTBA.textBox.Text,
                    EName = enTBA.textBox.Text,
                    AName = anTBA.textBox.Text,
                    CareerCode = careerCodeCBA.comboBox.SelectedItem.ToString(),
                    Specialization = specTBA.textBox.Text,
                    Mobile = mobileTBA.textBox.Text,
                    Telephone = teleTBA.textBox.Text,
                    Email = emailTBA.textBox.Text
                };
                db.employees.Add(employee);
                db.SaveChanges();
            }
            catch (DbUpdateException exception)
            {
                MessageBox.Show(exception.InnerException.InnerException.Message);
            }
            catch (EntityException exception)
            {
                MessageBox.Show(exception.InnerException.Message);
            }
        }