<?php
function list_terms_listings( $atts ) {

	   $a = shortcode_atts( array(
        'id' => 10
    ), $atts );

$term_id = $a['id'];
$taxonomy_name = 'listing_category';
$termchildren = get_terms( array(
    'taxonomy' => $taxonomy_name,
    'hide_empty' => false,
    'orderby' => 'name',
    'parent' => $term_id
) );

$mainCat = get_term_by('id', $term_id, $taxonomy_name);

echo '<h2><a href="' . get_term_link( $term_id, $taxonomy_name ) . '">'.$mainCat->name.'</h2>';
echo '<ul>';
foreach ( $termchildren as $child ) {
	$term = get_term_by( 'id', $child, $taxonomy_name );
	echo '<li><a href="' . get_term_link( $child, $taxonomy_name ) . '">' . $term->name . '</a></li>';
	$termchildrenlvl1 = get_terms( array(
    'taxonomy' => $taxonomy_name,
    'hide_empty' => false,
    'orderby' => 'name',
    'child_of' => $child->id
) );
	if ($termchildrenlvl1 == true) {
		echo '<ul>';
	foreach ($termchildrenlvl1 as $termchildlvl1) {
		$termlvel1 = get_term_by( 'id', $termchildlvl1, $taxonomy_name );
	echo '<li><a href="' . get_term_link( $termchildlvl1, $taxonomy_name ) . '">' . $termlvel1->name . '</a></li>';

		}
		echo '</ul>';
	}
}
echo '</ul>';

}
// Add a shortcode that executes our function
add_shortcode( 'dr_terms', 'list_terms_listings' );