how to treat cash deposit 20lakh

depend on your reply if you are explain then 44 AD if u are not explain then whole amount

General thing- When something is caught as undisclosed then all you could do is respond to the notice u/s 148 and not start filing the revised return after income is getting caught.

Now coming to your question; If you have deposited something in your account then you must have the knowledge about the source of it. And if you are able to explain this cash deposit through cross checks of your accounts and also prove that this income has already been considered while filing the return then there is nothing to be worried about.

But if you are not able to explain that.. then AO would assess that as Cash Credit U/s 115BBE and you have to pay huge tax and Penalty which comes around 85% in Aggregate.