@murielle I was going for a mix of "boring" and "interesting" in those thumbnails. They mention in the class that sometimes you want boring, and since I often need to make background elements that blend in the boring stuff is important for me too.
I don't disagree on the trees. I probably could have made more of those interesting. I tend to try and make my distinctions on the vertical shapes for those. I think the problem is that trees tend to be pretty evenly distributed (at least horizontally) in real life.
I went for a walk after reading your comment and took a good look at all of the trees. Noticed that they are amazingly symmetrical in general. Pretty much all of the asymmetrical ones I spotted were forced that way by cutting. I guess being different would be what makes those one's interesting though. 