Robert M. Gary writes:

I don't find that whether the trees look like lumps of green or have
leaves on them makes one bit of difference to a real simulator.

That's not the important part. The important part is that everything in the
cockpit must look as it does in real life, since much of the training (in the
case of airline pilots, for example) is intended to reinforce procedures that
are intimately connected to the ergonomy of the flight deck. It wouldn't do
to train pilots for engine failures on take-off using simulator cockpits that
have controls in positions different from those of the real thing--it would
defeat the entire purpose of the training, in fact. So these aspects are very
important.

What is outside the window, in contrast, is usually not important in these
types of simulations, although some things, such as airport surfaces, must be
accurately simulated.