Kadri, I isolated one tree from this file (006) in Blender (was a pain because the leaves of 2 trees are part of the same mesh) and exported the OBJ. Came out to 94MB. However, Poseray wanted to export it as some 200MB monster so I'd skip that step. Under 100MB per tree is not completely unreasonable, IMHO. The tree structure is certainly quite fine in this example, most of the low poly trees I've seen are (naturally) way simpler. They would also make nice bare/winter trees.