Runtime complexity of getting entries from BTreeMap Range

What is the big-O complexity of creating a std::collections::btree_map::Range from a BTreeMap of size N, and then reading K entries from the range?
My understanding is it should be O(log N + K) for theoretical B-Trees. Is this the case with std::collections::BTreeMap?

Indeed, I don't know of any complications that would loosen the log N + K bound.