code: @Override
    public TreeMap<Integer, IntervalST<Double, TreeMap<Integer, IScan>>> getMapMsLevel2rangeGroups() {
      return msLevel2rangeGroups;
    }
docs: Get a map, holding spectra groupped by precursor m/z isolation window. MS1 spectra are groupped
  by their overall m/z range.
  
  @return Interval search tree for every level, this is only created after a call to {@link
  #finalize()}. A call to {@link #finalize()} will be made for you automatically, if you load
  scans using an {@link LCMSDataSubset} with lo/hi scan nums as null.