This is a virtual beis medrash. A Beis Medrash is greater than a Shul. A Shul is like the Beis Hamikdash. One is not allowed to have a tree in the Beis Hamikdash, so kal vachomer not in a beis medrash. You will claim that this only a virtual tree, so it shouldn't be a problem. I'll answer that t...