The Bug
When you using a bone meal to grow a tree on a sapling planted on the moss block, it consumes the bone meal, but the sapling doesn't grow into a tree.
Step to Reproduce
1. Place down a moss block and place a sapling on it.
2. Bone meal it.
---> ❌ It shows particles and consumes the bone meal, but it doesn't grow into a tree.
This bug is considered a parity issue since the Java ones are already fixed for the next snapshot. (MC-213927)
This is fixed for all regular saplings, but not azalea or flowering azalea.
see MCPE-125767 for more details