I'm no expert, but it seems like you need to guess at some key ranges and start the BTree at some minimum size even if most of the leaves start out empty. Either that, or don't write anything until the tree grows a bit and rely on a writeahead log for durability.
Hotspots could still show up further down, though, if writes aren't fairly random.
Hotspots could still show up further down, though, if writes aren't fairly random.