Adding Arrow To Parent

How do I add an arrow (either code, image or class) to the parent of a submenu?

This is the code

<li><a href="<?php bloginfo('url'); ?>/link" class="nav" id="nav2">Link</a>

		<?php

			$children = wp_list_pages('title_li=&child_of=26&echo=0&sort_column=menu_order');
			if ($children) {  

		?>
		<ul>
			<?php echo $children; ?>
		</ul>
		<?php } ?>
		</li>

I didn’t write this code, just trying to edit. I did try this: but it didn’t work
https://blogmum.com/2009/09/how-to-find-if-a-wordpress-page-has-children/