I've personally used a B+Tree variant in this case with special-cased insert rules. Rather than splitting nodes when they're full, if they're filled due to appe

I've personally used a B+Tree variant in this case with special-cased insert rules. Rather than splitting nodes when they're full, if they're filled due to appending at the right-hand-side we simply start the next leaf (or next interior + leaf pair) during insert. So, for pure in-order insertions, we end up with a maximally efficient tree with no splits needed; the rest of the logic still works if you then go back and need to update or insert into the middle of the tree at a later date. I'm sure I'm not the only one with that particular implementation, but I'm not aware of any named algorithm/variant for it.