Are their flowers, birds and trees in heaven?

Who knows, no one has ever returned.

There is no one that knows, examples of heaven are that of visions of a future that they could not understand fully when they had the vision.
The issue is, it does not matter, it may be far past such things.

No one knows how heaven does look like. But there are some philosophical approaches describing heaven as a paradise. Maybe there isn't something like a heaven. It's a very difficult question to answer.