Affects Version/s: Minecraft 18w47a
Fix Version/s: None
OS: Windows 10,
Java version: bundled java runtime
2G memory allotted to game via JVM arguments in launcher
Some of the trees seem to have generated on dirt pillars and/or with dirt in the trunks. This does not appear to be a duplication of https://bugs.mojang.com/browse/MC-125807 as not all the logs in the chunk have been replaced by dirt, the issue effects more than one type of tree, and what trees are effected seems undefined by what chunk they are in.
The dirt/logs mix varies tree to tree, some are unaffected, some have just a few dirt blocks, and some have more dirt than logs. I have also seen trees with dirt where there should be no block at all.
The dirt is removeable, and drops as dirt, the logs drop as logs, and I can place logs where the dirt was just fine.
This cannot have been endermen, as I just teleported to the chunk in search of a pillager hideout, so there would not have been time. It is also insufficiently randomized for endermen behaviour.
I did however teleport into a nearby chunk without having previously generated it, instead of walking in. I don't know if that has an effect.
A few screenshots of the issue are located in the attachments, including one with the debug screen open for further information.