Baumkuchen is German. But for whatever reason, in Japan it is wildly popular. You can find it pretty much everywhere, from specialty shops to grocery stores, to omiyage shops to conbini. This is one of the things that has surprised me living in Japan and I have started to consider baumkuchen more of a Japanese thing than an actual German thing. I have probably eaten dozens of the single-serving snack baumkuchen since living here.
Baumkuchen means “tree cake” since the cute round shape shows rings similar to tree trunks. The taste is pretty typical of a cake with packed thin layers, and often you can find different added flavors (chocolate, orange, etc). I have real idea why this snack/dessert is so popular here, but my guess is because the labor to make it is rather intensive, or time-consuming, and Japanese people have a deep appreciation for the skill and dedication to making such a creation. Respect for the hard-working spirit/attitude is very much a thing here, so I get the impression that this little cake is sort of a symbol of that.
My sensei has leftovers from Obon, so he brought some in for us.