Calculate QTY column as function of father-son relationship (as defined by A column)

[Zadok]

Hi,

Looking for a way to automaticaly calculate the "actual" QTY per line, of hierarchical list (father-son relationships).
Column A defined the relationships, where father has a higher "rank" (for example if son rank is "4" then his father is "3", and so on).
The calculation of a son QTY, is multiplications of all father's QTYs along the chain, upto rank "1".

Please see attched file, the 2nd table is the required calculated results of upper table.

Thanks,
Zadok