The April 2022 cover of Nature Biotechnology, by Martin Krzywinski — a tree of 235 million sequences drawn as cherry blossoms. Each blossom is a circle packed with circles, packed with smaller circles. Here the packing is driven by π: each digit says how many circles nest inside the next. Five levels deep, the last lit bright green against the purple — just like his cover. The idea and the mathematics are his; we built this toy to feel the packing from the inside.