def add_root_objective_bank(self, alias=None, objective_bank_id=None):
url_path = self._urls.roots(alias=alias)<EOL>current_root_ids = self._get_request(url_path)['<STR_LIT>']<EOL>current_root_ids.append(str(objective_bank_id))<EOL>new_root_ids = {<EOL>'<STR_LIT>': current_root_ids<EOL>}<EOL>return self._put_request(url_path, new_root_ids)<EOL>
Adds a root objective bank.

        arg:    objective_bank_id (osid.id.Id): the ``Id`` of an
                objective bank
        raise:  AlreadyExists - ``objective_bank_id`` is already in
                hierarchy
        raise:  NotFound - ``objective_bank_id`` not found
        raise:  NullArgument - ``objective_bank_id`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        *compliance: mandatory -- This method must be implemented.*