Expandable Categories 1.0
It works best with root categories as headings enabled.
It is released under the GPLv3 and may be released under a different license with permission.
$Configuration['Plugins']['ExpandableCategories']['ExpandActiveOnLoad'] = FALSE; in your
/conf/config.php file will keep the full list collapsed on page load.
Tested working on 2.0.18.x and 2.1