this is mostly working, but due to some issue with leaf decay, the edges of the larger canopy will decay within minutes.
I don't know why this is yet, but it's likely some incorrect implementation of Leaves causing the problem.
In addition, the secondary branch of acacia may generate next to the base block of the trunk, which I've never observed to happen in vanilla. This has a 2% chance of occurring, so I haven't been able to rule it out yet, but it probably shouldn't happen.
TreeType includes a bunch of stuff that don't have regular saplings associated with them, such as mangrove and azalea trees.
Mangrove has a dedicated propagule block with different behaviour than the others, and azalea trees are grown from azalea blocks, which are solid and have different behaviour to saplings.
We may also want to account for crimson and warped 'trees' in TreeType too, although I'm not sure if those belong there or not.
