I have always thought that the tree on five was something of an icon. It has a great shape and really adds some character to the hole, not that the fifth needs anymore.
However, I think the tree takes the players attention away from the truly "safe" route on this hole. For all intents and purposes, the bunker on the far right is out of play unless you play over the tree. Granted, I played CD by myself, so I don't know how others would play the hole, but my guess would be, that most consider aiming between the large bunker on the left and the tree. This puts the center line of the fairway right through the Three Sisters.
Now, if the tree was not there, there would be a large open space between the Three Sisters and the bunker on the right, making for an "easy route". However, technology has transformed this hole slightly, making it fairly easy to hit a three iron to about a hundred yards.
Nonetheless, the solitary trees on the front nine at CD, just add to the experience. Nothing was more thrilling to me then shaping a perfect little cut between the two trees on the left and the lone tree on the right of number six. Solitary trees do make for interesting strategic decisions, and add in this case, even more character to a course thats already full of great charm and character. In Crystal Downs we trust, all others aspire!!!