code: def start_multiplex_socket(self, streams, callback):
          
          stream_path = 'streams={}'.format('/'.join(streams))
          return self._start_socket(stream_path, callback, 'stream?')
docs: Start a multiplexed socket using a list of socket names.
          User stream sockets can not be included.
  
          Symbols in socket name must be lowercase i.e bnbbtc@aggTrade, neobtc@ticker
  
          Combined stream events are wrapped as follows: {"stream":"<streamName>","data":<rawPayload>}
  
          https://github.com/binance-exchange/binance-official-api-docs/blob/master/web-socket-streams.md
  
          :param streams: list of stream names in lower case
          :type streams: list
          :param callback: callback function to handle messages
          :type callback: function
  
          :returns: connection key string if successful, False otherwise
  
          Message Format - see Binance API docs for all types