Bushes generate in the air very commonly. This bug was also in the previous versions of the game and I still don't see the fix being implemented.
MC-168101
Floating bushes over small lakes
Resolved
Duplicate
0
Simon
(Unassigned)
Unconfirmed
(Unassigned)
1.15
Retrieved
This has been in the game for i think a couple years now, I see it as a more funny quirk or glitch, like the 'spycrab' model glitch from Team Fortress 2