One of my skyblock players noticed the saw doesn't work on warped fungus. It seems like something that would be sensible to add to the tree chopping logic..

Which Minecraft version is it?

Sorry, didn't think it mattered. 1.20.1. Latest version of every mod as of this morning. I thought it would be nice if the saw worked on all the huge mushrooms/fungi. So: red mushroom, brown mushroom, crimson fungus, and warped fungus. The fungus was added in 1.16.0. Of course the red and brown huge mushrooms have been in the game for eons but there usually isn't much reason to think of them unless some packs and mods make a point of using them.