only show parent category in channel form

{exp:channel:form channel="training_institutions" url_title="{segment_3}" author_only="yes"  datepicker="no" return="training-program/update/success"}
{category_menu}
  <label for="categories">Country</label>
<select name="category[]" id="categories">
  {categories}
    <option value="{category_id}"{selected}>{category_name}</option>
  {/categories}
</select>

       
{/category_menu}

{/exp:channel:form}