In my game, the characters are drawn from a birds eye view (including the player) and the player moves in a top down fashion, with rotation relative to the mouse (i.e it faces the mosue).

This is a rather general question regarding not only my game but 2D, top-down games in general.

Do you think it makes sense and is aesthetically pleasing to draw landscape features from a level-eye view even though the characters are drawn from a birds eye view?

The reason I ask is because I'm finding it hard to find or produce things such as trees and even rocks that look recognizable from a birds eye perspective.

Would it be acceptable to just draw the environment from a horizontal level-view?  If not, do you have any suggestions for what to do with drawing them from the birds eye view?

You could just draw the terrain in 3D. Example: Ragnarok Online

It's usually the other way around though. Both characters and terrain are drawn from above but at a certain angle (Gameboy Pokemon games, old Final Fantasy games, anything using tilesets >_>).

Angles require 3D rendering.  This game is entirely 2D.  So it's either top/down from the top, top/down from the side or left/right.

I found a picture of a real tree online from a birds eye view.  It showed enough of the branches and trunk that it could be recognized as more than a bush, which is what I was looking for/trying to create.

I then just used some sharpening effects in Paint.NET to make it fit more of the 2D game style of graphics rather than look perfectly realistic.  Seems to work fine.