code: public static Map<String, ISettings> mergeSettings( Map<String, ISettings> old, Experiment experiment )
    {
      Map<String, ISettings> defaultSettings = makeDefaultSettings( experiment );
      old.keySet().forEach( key -> defaultSettings.put( key, old.get( key ) ) );
      return defaultSettings;
    }
docs: Assumes settings map is ordered top-down in tree order