The new waveform group. This parameter cannot be null.
The zero-based index at which the new waveform group should be added. The value -1 indicates to add the group at the end.
In DICOM, a waveform consists of one or more multiplex groups, each encoded into an item in the "Waveform Sequence" (5400,0100). Call this method to add a new multiplex group to the Data Set.
For an example, refer to WaveformGroupCount.