Sorry, you can't use hierarchy in SELECT or FILTER!
If you have multiple hierarchies and you need to select members under parents of PARENTH1 then:
For example in PARENTH1 you have 2 root parents: P1 and P2
*XDIM_MEMBERSET COMPANYCODE=BAS(P1,P2)
Vadim
P.S. It's better to provide the detailed explanation of your COMPANYCODE dimension to get help...