How to have a selected item in ion-select?

I have an ion-select which can select multiple options and i am setting the first option as selected initially using below code:

<ion-select interface="popover" class="note-select-list-documents"
     <ion-option *ngFor="let option of question.PickListOptions; let i = index"

Now, initially one option will remain selected but user can deselect that options. But, i want that there will always be one item selected. If user have option selected, then user can deselect one but when one item is selected, user can not deselect it.

Is there any control on ion-select to achieve this scenario?