javascript - multiple ng-Options are showing all together as text box Any idea Why? -

i have multiselect requirement, here happening on page load multselect values showing in in select box , how can show dropdown , if user select value value should display in select..

main.html

 <select         class="form-control"         multiple         name="themeslist"         id="themeslist"         ng-model="challengesdto.themeskylist"         required         ng-options="option.id option.text option in challengoptions">         <option value="">             select...         </option>     </select>