The bug

When a tree generates from a sapling it can occasionally spawn with a bee nest, if it is placed in a biome that bee hives can spawn in. This is likely because bee nests were added straight into the tree model so any means of generating a tree can cause them to spawn.

This causes issues with tree farms, as bee hives are not movable by pistons.

To reproduce

1. Find a plains biome
2. Place a sapling
3. Bone meal it
   → Occasionally, the tree will have a bee hive