Well, it's actually a tree, rabbit and turtle wedding cake, but "Tree and Turtle" is more alliterative.
This was for a couple who had reconnected after years apart, so they weren't looking for a traditional white wedding cake. Everything on this cake had some meaning to them, so it was a completely personalized design. Which is how a wedding cake should be.
I got a nice thank you note a few days after the reception. "...The symbols were perfect, the taste divine..."
So use things on your cake that mean something to you, and don't worry if it's traditional or not. If it has meaning for you, go for it!