Bamboo steamer

Mushiki (蒸し器, literally: steam-vessel) or seiro (蒸籠, literally: steam-basket) are two different types of vessels used for steaming in Japanese cuisine.

Mushiki are round steamers made from bamboo like those used in Chinese cuisine. They can be stacked on top of each other so that the steam can cook many different servings simultaneously. Seiro are large rectangular steamers made traditionally from bamboo but nowadays also often from metal. Seiro can also be stacked.

...
Wikipedia