def trigger(self, username, project, branch, **build_params):
        """Trigger new build and return a summary of the build."""
        method = 'POST'
        url = ('/project/{username}/{project}/tree/{branch}?'
               'circle-token={token}'.format(
                   username=username, project=project,
                   branch=branch, token=self.client.api_token))

        if build_params is not None:
            json_data = self.client.request(method, url,
                                            build_parameters=build_params)
        else:
            json_data = self.client.request(method, url)
        return json_data
Trigger new build and return a summary of the build.