The bug
When trees generate near a mushroom biome in 1.15 Pre-Release 1, they can generate on mycelium unlike in 1.14.4 and earlier.
How to reproduce
This glitch is found using the seed 5878760421836343227 and the coordinates 65 79 32 (for an oak tree) and -1 79 3 (for a jungle tree), and notice at these coordinates the tree spawned directly in a mushroom biome.
Linked issues
relates to 1
Attachments
Comments 2
Can confirm in 21w16a. You can grow trees on mycelium, so it may be intentional.
gaspoweredpick
Relates to MC-610, but it happened later so it's not the same bug.