Nav bar is hiding the menu icons!

Somehow I can’t get the button to show on the nav bar. I think this is a very simple code, but why it doesn’t work?

<ion-pane ion-side-menu-content>
    <ion-nav-bar class="bar-balanced">
      <button menu-toggle="left" class="button button-icon icon ion-navicon"></button>
    </ion-nav-bar>
</ion-pane>