code: def _add_trustee(self, device):
          '''Add a single trusted device to the trust domain.
  
          :param device: ManagementRoot object -- device to add to trust domain
          '''
  
          device_name = get_device_info(device).name
          if device_name in self.domain:
              msg = 'Device: %r is already in this trust domain.' % device_name
              raise DeviceAlreadyInTrustDomain(msg)
          self._modify_trust(self.devices[0], self._get_add_trustee_cmd, devicef _add_trustee(self, device):
          '''Add a single trusted device to the trust domain.
  
          :param device: ManagementRoot object -- device to add to trust domain
          '''
  
          device_name = get_device_info(device).name
          if device_name in self.domain:
              msg = 'Device: %r is already in this trust domain.' % device_name
              raise DeviceAlreadyInTrustDomain(msg)
          self._modify_trust(self.devices[0], self._get_add_trustee_cmd, device)
docs: Add a single trusted device to the trust domain.
  
          :param device: ManagementRoot object -- device to add to trust domain