Wp Dtree

where should i put this code
ref: http://wordpress.org/extend/plugins/wp-dtree-30/installation/
Displaying categories:

• <h2>Categories</h2>

<?php
if (function_exists(‘wp_dtree_get_categories’)){
wp_dtree_get_categories();
}else{
wp_list_categories(‘show_count=1’);
}
?>