travel between dhaka and bangalore

Hi

Am planning a trip to Dhaka and Bangalore (from Geneva, Switzerland,
where I live). I need to go to Dhaka first and then Bangalore, but
then would like to come right back. Does anyone have advice on whether
I should buy
1. an open jaw ticket: Geneva to Dhaka to Bangalore to Geneva
or
2. a round-trip Geneva-Dhaka and a separate ticket for the
Dhaka-Bangalore round-trip (it seems one can only fly via Cal). Not
having any experience with buying tickets in Bangaldesh, I don't know
whether this is the cheaper option.

Thanks for any tips.
S