After some searching and noclipping around the underwater condo, I have found the "odd tree". Seeing as how there is no guide for this achievement, I decided to quickly put this one together.
The General Idea of Where the Tree Can Be Found
First of all you want to go to satellite condo 4:
Then you move to about here. The left island is satellite condo 4, the middle island is the central condo and the right island is satellite condo 3, as a reference point for this image:
Once you're in this general area in the middle of the water, you're going to want to go straight down. You're end goal is to look for this:
That's pretty much it. Try searching near the edge of the map.