WaikatoDHB webmaster on "Converting a bullet list to a select box"

Hi. I'm currently using the Meet the team plugin The filter option displays in bullet form as you can see here.

How can i convert the below code to make this a dropdown box with an onchange instead?

<ul id="wpmtp-source-'. $unique  .'"><li>Filter by: <a href="#" class="wpmtp-all">Show all</a></li>&bull; ';

     	$tax = get_terms("team-category");
     	foreach ($tax as $tax_term) {
     		$return_string .= '<li><a href="#" class="filter-' . $tax_term->slug . '">'. $tax_term->name .'</a></li>&bull; ';
     	}

        $return_string .= '</ul>