What custom did Natchez tribesmen volunteer for when their chief died?

Ritual sucide

Explanation:

The Natchez are a Native American people that lived in Mississippi before the colonists took the land. After some wars against the French they were dispersed with a large number sold into slavery by the French and most of the rest joining the Cherokee and Muscogee.

In times past they were ruled by the Great Sun and when he died, his wives were expected to commit sucide to be with him. Tribesmen would also volunteer to commit ritual sucide to be with him as well as it was considered to be a great honor to do so.