GetRootNodes.
        [Preview API] Gets root classification nodes under the project.
        :param str project: Project ID or project name
        :param int depth: Depth of children to fetch.
        :rtype: [WorkItemClassificationNode]

def get_root_nodes(self, project, depth=None):
        """GetRootNodes.
        [Preview API] Gets root classification nodes under the project.
        :param str project: Project ID or project name
        :param int depth: Depth of children to fetch.
        :rtype: [WorkItemClassificationNode]
        """
        route_values = {}
        if project is not None:
            route_values['project'] = self._serialize.url('project', project, 'str')
        query_parameters = {}
        if depth is not None:
            query_parameters['$depth'] = self._serialize.query('depth', depth, 'int')
        response = self._send(http_method='GET',
                              location_id='a70579d1-f53a-48ee-a5be-7be8659023b9',
                              version='5.1-preview.2',
                              route_values=route_values,
                              query_parameters=query_parameters)
        return self._deserialize('[WorkItemClassificationNode]', self._unwrap_collection(response))