Missing Ion-slide pager when have ion-slides in ion-slide (slides in slides)

I have main ion-slides and in ion-slide page has sub ion-slides
and it show only pager of sub ion-slides ,main pager ion-slides missing

 <ion-slides pager style="height: 20em;">
      <ion-slide style="border: 1px solid blue">
        Slide 1
      </ion-slide>
      <ion-slide style="border: 1px solid blue">
        Slide 2
        <ion-slides pager style="height: 10em;">
          <ion-slide style="border: 1px solid brown">
            sub Slide 1 in Slide 2
          </ion-slide>
          <ion-slide style="border: 1px solid brown">
            sub Slide 2 in Slide 2
          </ion-slide>
          <ion-slide style="border: 1px solid brown">
            sub Slide 3 in Slide 2
          </ion-slide>
        </ion-slides> 
      </ion-slide>
      <ion-slide style="border: 1px solid blue">
        Slide 3
      </ion-slide>
    </ion-slides>

screen issue
pager-issue

but if has only main ion-slides ,pager work properly

 <ion-slides pager style="height: 20em;">
      <ion-slide style="border: 1px solid blue">
        Slide 1
      </ion-slide>
      <ion-slide style="border: 1px solid blue">
        Slide 2
       <!--
        <ion-slides pager style="height: 10em;">
          <ion-slide style="border: 1px solid brown">
            sub Slide 1 in Slide 2
          </ion-slide>
          <ion-slide style="border: 1px solid brown">
            sub Slide 2 in Slide 2
          </ion-slide>
          <ion-slide style="border: 1px solid brown">
            sub Slide 3 in Slide 2
          </ion-slide>
        </ion-slides>
        --> 
      </ion-slide>
      <ion-slide style="border: 1px solid blue">
        Slide 3
      </ion-slide>
    </ion-slides>

screen work properly
work-properly

please help, how to make it have pager both of main ion-slides and sub ion-slides