"Birthday cake made of fruit" No. Not a cake. Just a big slice of watermelon with some pretty fruit on it. And if you try to serve this to me as my birthday cake, clearly you are asking to be ridiculed for the rest of your natural life.
DIY Party Idea - Stacked Fresh Watermelon Cake- for summer birthday parties! Just cut the watermelon in "cake" like pieces as shown in the picture.insert fruit skewers into the "cake" and enjoy! Picture only.