Based on one of GWCode Categories examples I have created code below
<li class="submenu-parent">
<a href="#">Product Type</a>
<div class="submenu cf" id="submenu-1">
{exp:gwcode_categories channel="products" style="linear"}
{if depth1_start}<h3>{cat_name}</h3>{/if}
{/exp:gwcode_categories}
</div>
</li>
but it pulls only 2 first parent (root) categories from 12 categories assigned to the products channel.
Any clue?