Anyone know if there's a way I can collapse multiple values onto the same line?

For example, in my GANTT chart I have the following scenario. The
horizontal category is multi-level, Brand + Promotion Name. I'd really like
to be able to collapse scenarios where there's multiple records, with the
same or different values, into single lines. For example, in the example
below, I'd like to put the two brand = El Jimador, promotion = Paloma entries
onto one line.

Multi-level category label for both entries is El Jimador + Paloma

Entry 1: Start Date = Jan1 , Duration 60
Entry 2: Start Date = Mar1, Duration = 60

So ideally, I would end up with one line with both durations filled in. Any
thoughts?
Thanks.
Ivano