It seems not to work with existing labels whose names contain a slash, even if you rename those labels. Also note that the parent label must exist, e.g. to hav

It seems not to work with existing labels whose names contain a slash, even if you rename those labels. Also note that the parent label must exist, e.g. to have "people/friend-a" and "people/friend-b" appear in a hierarchy, you must also have a "people" label.