I was curious to know if I could get a placed sapling to instantly spawn a tree. I've looked at the classes Block and BlockState but I'm not too sure which to use, if either.
You'd want to watch for a placement, as soon as someone places a sapling grow a tree in that location.
I did this by watching for the block placement, cancelling the event, and calling world.generateBigTree() on the location. It's pretty fun