docs: def add_datetime(dataframe, timestamp_key='UNIXTIME'):
      """Add an additional DATETIME column with standar datetime format.
  
      This currently manipulates the incoming DataFrame!
      """
  
      def convert_data(timestamp):
          return datetime.fromtimestamp(float(timestamp) / 1e3, UTC_TZ)
  
      try:
          log.debug("Adding DATETIME column to the data")
          converted = dataframe[timestamp_key].apply(convert_data)
          dataframe['DATETIME'] = converted
      except KeyError:
          log.warning("Could not add DATETIME column")