Custom Taxonomy Tree view

<?php
$args = array(
  'taxonomy'     => 'product-type',
  'hierarchical' => true,
  'title_li'     => '',
  'hide_empty'   => false
);
?>

<ul>
<?php wp_list_categories( $args ); ?>
</ul>

You can use the wp_list_categories function also for taxonomies. http://codex.wordpress.org/Template_Tags/wp_list_categories