The phrase "added on top" is correct and usable in written English.
You can use it to indicate that one thing has been added to something else. For example: "We added some extra cheese on top of the pizza."
The gravy can be added on top of either one.
In other words, only one additional biologist can be added on top of the original default number of 1.
A concrete block was added on top in the 1960s.
Drummond said the NO2 tax should be added on top.
Thinking, feeling, all those other things are added on top of that.
Sometimes a subsidiary human face was added on top of the head.
But the iron fences remain, some with fresh spikes added on top.
The completely unlistenable Linkin Park is basically very loud Depeche Mode with bad rapping added on top.
At the Senate hearing last week, he called the rule unnecessary when "added on top of other stuff".
"I thought it was unnecessary when it was added on top of other stuff," Mr. Dimon responded.
Compensation will be added on top for the distress caused.
