Taxonomy Term Hierarchy(not programmatically nor content related)
you can use the Views Tree module for this: https://www.drupal.org/project/views_tree

It works pretty well, you just need to use the Tree (list) views FORMAT, add the parent taxonomy term in RELATIONSHIPS, add the parent term's Name field to the FIELDS list, and then use it as the Parent field on the Tree settings:



The module will link the terms hierarchically and output a nested list, and you can always hide the parent term's name field to show just the children terms names.