There are currently only two advancements in this mod, so I'd like to have some more.
Here are my suggestions:

• "Bonsai Master" - Grow all Vanilla trees
  • This would require the player to find every single plant type in the game
• "Hopping Bonsai Pot" - Craft a Hopping Bonsai Pot
  • Since we already have an advancement for crafting the regular pot
• "Bonsai Factory" (or "Bonsai Farm") - Have 10 or more active Hopping Bonsai Pots at the same time
  • I'd imagine that some players are likely to have this setup if they want a tree farm

Advancements for trees from other mods would also be great, but I don't know if advancements can be enabled depending on if certain mods are installed or not.