Questions

Can I use it with only vanilla? Yes, it can be completed that way but it was not designed for that, and a lot of the tree is missing without other mods.

Does it work on Fabric or Forge? NeoForge 1.21.1 only.

Does it work in single player? Yes, but it will be tough…

Can I change the tree? The whole tree is one JSON file, tree.json. So yes. You can adjust it if you know a bit of coding. Do not republish the modified tree mod.