Data Text to Columns Comma Delimiter produces this:

129 A B C D
129 A C G

Pivot Table Multiple Consolidation Ranges
Range: Select the data plus an empty row above.
Layout drag Column button from the diagram and
replace it with Value.
Options: Uncheck sums
Part of the pivot table will look like this:

A B C D G
2 1 2 1 1

If the A in the pivot table is at D4 then enter at J4
=D4
At K4 enter
=CONCATENATE(J4,",",E4)
and fill adjacent cell until you get
A A,B A,B,C A,B,C,D A,B,C,D,G