Did you know there's one in DBA ? (BM-C)
 
If you need to do it in Crystal, use BKBMMSTR.Bxx file.  Choose fields BKBM_PARENT, BKBM_COMPONENT and BKBM_QTY_REQD.  Group on COMPONENT and you'll get a simple, one level report.  Further grouping will go into deeper levels.
 
You can link to BKICMSTR.Bxx for Description fields.