code: def netconf_session_start_username(self, **kwargs):
          
          config = ET.Element("config")
          netconf_session_start = ET.SubElement(config, "netconf-session-start", xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-notifications")
          username = ET.SubElement(netconf_session_start, "username")
          username.text = kwargs.pop('username')
  
          callback = kwargs.pop('callback', self._callback)
          return callback(config)
docs: Auto Generated Code