Factorio Forums

if you hold a train stop, it will show you possible places you can put it, unless there is something in the way (like a belt or a tree).
However, if a tree is a bit to the side of the place, it might still be possible to place a train stop on that position, even though there isn't a green square to signify it: I think it is problem with the green square using the wrong hit box to check whether a stop can be placed there.

Can you upload a small (50x50) example map that shows the issue?

you can place at the top of the rails (between the trees), but it does not show a square there.

Fixed for 0.15.