Is Bangalore in a real estate Bubble ?

May be or may be not. Can't say. But real estate is in bull market definitely.

Wait till the Bangalore home owners realise that people are willing to pay more than 2x of current rent, that would constitute a bubble. (Similar to Mumbai)

The only reason stopping that from happening is that Mumbai is water locked and can expand in one direction only, whereas Bangalore can expand in multiple directions, hence the rent and house price increment is somewhat nominal only.

The exorbitant price increase is most likely limited to a few areas, where the rich founders and executive live.

So, most likely not a bubble.