Get Parent -> Child Terms (With or Without Custom Taxonomy)

gistfile1.txt

<nav>
    <?php
    foreach( get_terms( 'tax_pipeline', array( 'hide_empty' => true, 'parent' => 0 ) ) as $parent_term ) {
        // display top level term name
        echo $parent_term->name . '<br>';

        foreach( get_terms( 'tax_pipeline', array( 'hide_empty' => true, 'parent' => $parent_term->term_id ) ) as $child_term ) {
          // display name of all childs of the parent term
          echo '>>>>>' . $child_term->name . '<br>';
        }

      }
    ?>
</nav>

CAN BE SIMPLIFIED TO

<?php wp_list_categories( 'taxonomy=tax_pipeline' ); ?>