The implementation of `BTreeMap::append` is non-performant making merging changesets very slow. We use `Extend::extend` instead. Refer to: https://github.com/rust-lang/rust/issues/34666#issuecomment-675658420
The implementation of `BTreeMap::append` is non-performant making merging changesets very slow. We use `Extend::extend` instead. Refer to: https://github.com/rust-lang/rust/issues/34666#issuecomment-675658420