Create a new page template called CATLIST and copy the contents below into that template.

<select name="Category_Code">
<option value=""> All Categories</option>
<mvt:item name="toolkit" param="parentcat|pccount" />
<!-- check for parent cats //-->
<mvt:foreach iterator="parent_category" array="parent_categories">
<mvt:if expr="g.Category_Code EQ l.settings:parent_category:code">
<option value="&mvte:parent_category:code;" selected>
&mvt:parent_category:name;</option>
<mvt:else>
<option value="&mvte:parent_category:code;">
&mvt:parent_category:name;</option>
</mvt:if>
<!-- check for 1st level subcats //-->
<mvt:item name="toolkit" param="subcat|ccount|l.all_settings:parent_category:code" />
<mvt:if expr="ccount GT 0">
<mvt:foreach iterator="sub_category" array="sub_categories">
<mvt:if expr="g.Category_Code EQ l.settings:sub_category:code">
<option value="&mvte:sub_category:code;" selected>
&nbsp;&mvt:sub_category:name;</option>
<mvt:else>
<option value="&mvte:sub_category:code;">
&nbsp;&mvt:sub_category:name;</option>
</mvt:if>
<!-- check for 2nd level subcats //-->
<mvt:item name="toolkit" param="subcat2|ccount2|l.all_settings:sub_category:code" />
<mvt:if expr="ccount2 GT 0">
<mvt:foreach iterator="sub_category2" array="sub_categories2">
<mvt:if expr="g.Category_Code EQ l.settings:sub_category2:code">
<option value="&mvte:sub_category2:code;" selected>
&nbsp;&nbsp;&mvt:sub_category2:name;</option>
<mvt:else>
<option value="&mvte:sub_category2:code;">
&nbsp;&nbsp;&mvt:sub_category2:name;</option>
</mvt:if>
<!-- check for 3rd level subcats //-->
<mvt:item name="toolkit" param="subcat3|ccount3|l.all_settings:sub_category2:code" />
<mvt:if expr="ccount3 GT 0">
<mvt:foreach iterator="sub_category3" array="sub_categories3">
<mvt:if expr="g.Category_Code EQ l.settings:sub_category3:code">
<option value="&mvte:sub_category3:code;" selected>
&nbsp;&nbsp;&nbsp;&mvt:sub_category3:name;</option>
<mvt:else>
<option value="&mvte:sub_category3:code;">
&nbsp;&nbsp;&nbsp;&mvt:sub_category3:name;</option>
</mvt:if>
<!-- check for 4th level subcats //-->
<mvt:item name="toolkit" param="subcat4|ccount4|l.all_settings:sub_category3:code" />
<mvt:if expr="ccount4 GT 0">
<mvt:foreach iterator="sub_category4" array="sub_categories4">
<mvt:if expr="g.Category_Code EQ l.settings:sub_category4:code">
<option value="&mvte:sub_category4:code;" selected>
&nbsp;&nbsp;&nbsp;&nbsp;&mvt:sub_category4:name;</option>
<mvt:else>
<option value="&mvte:sub_category4:code;">
&nbsp;&nbsp;&nbsp;&nbsp;&mvt:sub_category4:name;</option>
</mvt:if>
</mvt:foreach>
</mvt:if>
</mvt:foreach>
</mvt:if>
</mvt:foreach>
</mvt:if>
</mvt:foreach>
</mvt:if>
</mvt:foreach>
</select>