Need some creative suggestions

[nekomeh]

I am building a dart frog tank out ivan old 55 gallon aquarium. My wife and I thought it would be nice if we could build a waterfall in one corner and make a "tree" in the other corner. We can't figure out a good way to make the tree. I've seen where someone used great stuff foam and covered it in coconut fiber, but that is what we had planned on doing for the rest of the background so the plants would have something to hang on to. Any suggestions?