I'm certainly not an anatomy expert. Did you know this or did you just look it up after reading this thread? 
I did not remember exactly what's going on there, though I have heard of that before. I've seen discussions on forums a long time ago about this and how it's fascia, not muscle causing this "wavy" effect. Some genetically have more of this, others don't get the Christmas Tree even at similar fat levels.
Ofcourse, I don't have the all the latin names memorized I looked that up. But I do understand how most muscles inserts and pulls becuase I have been interested in muscle anatomy in younger years and have done several courses involving anatomy.
About how some get the christmas tree and others don't it has more to do with lat development, insertions and bodyfat distribution. For example bodybuilders like Dorian, Flex and Shawn Ray had really thick lat development and naturally it will be more pronounced and defined.
Where as someone Like Dennis Wolf had very poor lat development and high insertions and it can hardly even be seen.
Also it seems to be common that bodybuilders in later years tears or pulls their lover lats. I remember from what I could tell Cutler tore or strained his lat I believe because at some point he had no xmas tree anymore, but he did have it earlier like before 03-04 or so.
Example of Jay's pulled lat before and after. Left side lat the most, but right side has pulled up some aswell:
