Images on Planes or Cubes

I was going over the bmesh benchmark test by Argus3D (simply amazing!) and I went through the comments (as best I could, 13 pages!) and I was wondering how the best way to get trees like that. I have tired the intersecting planes, but it looks…off at a certain size. I noticed he used what appeared to be cubes. I downloaded the .blend to make sense of it, to no use. I am not really new to Blender, I am new to taking it seriously. Thank you.

Cube is just a simplified representation of the complex object - if you switch blender to show each tree in detail while modeling landscape these billions would kill your pc… Blender would stop to respond.
There is a layer (see further) in mentioned file where it is just one such tree which is then duplicated by particle system thousands of times.
You can see it in detail (this won’t kill blender) if you check Display - Maximum Draw Type to Solid or Textured on Object tab - Cube icon.
Do not forget to switch it back to Bounds before you go to another layer (20 small square icons with/without circles in).