Baumkuchen is a traditional German cake which is very popular in Japan. Definitely the most famous German origin confectionery in Japan and everyone knows the name. On the other hand, many Germans do not know baumkuchen which can be translated to tree cake. Also it is quite hard to find baumkuchen at the stores in Germany.
Then, authentic German baumkuchen is different from the Japanese one. The shape is different and the taste is different. Therefore if you had eaten German baumkuchen in Germany, please try the Japanese version in Japan. Then, it is easier to find Japanese baumkuchen in Japan. It is also sold in 24/7 convienience stores too.