Related task upstream: Implement (tree) subtasks, as distinct from (graph) task dependencies
In Bugzilla I creates dependent bugs to form a tree of actions to do. Example for the Zuul upgrade a few months ago:
(dead link) https://bugzilla.wikimedia.org/showdependencytree.cgi?id=46176&hide_resolved=0
(See a working random example at https://bugzilla.mozilla.org/showdependencytree.cgi?id=836418&hide_resolved=0 )
Phabricator let us create sub tasks, I would love to see a deep tree representation of them.