This isn't what Wittgenstein means: form of life is a lot bigger. It's communal life and practice, so it would mean things like religious community, culture, and language. Right, but that doesn't tell us anything about the tree except as it relates to these professions within our communal form of life. All we can do is analyze the tree as it relates to our form of life: grammar, for Wittgenstein (and this is pretty much straight out of the Investigations) tells us what kind of thing anything is. To know what a thing is, we figure out what place it has in language. And according to their philosophy, they are well within theirs to try and unravel the conceptual confusions that led you to ask it. Part of this is also the attack on conceptions of reality. Interesting Wittgensteinians are usually inconsistent because Wittgenstein was opposed to interesting philosophy: he thought that if philosophy tells you something interesting or gives you new information, that it has gone off the rails and become confused, mistaking the shadows of language for the scaffolding of reality. Interesting philosophy is confused philosophy (to a certain degree, I would concur, by the way: Bishop Berkeley and Gottfried Leibniz had highly interesting philosophies that also happened to be incredibly confused). I'll try and take that as a compliment.