http://mmgen54p3ouu7zymz5u3mwoncsyfpqeamfaaupeordl6ogujslk7fjad.onion/project/mmgen/mmgen-wallet/wiki/Subwallets
However, this is inadvisable
in practice for two reasons: Firstly, it creates accounting complexity,
requiring the user to independently keep track of a derivation tree. More
importantly, however, it leads to the danger of Seed ID collisions between
subseeds at different levels of the hierarchy, as the software checks and avoids
ID collisions only among sibling subseeds and their parent....