How to show up button with actiontbar in Android UI when I push to sub-pages?

I'm using Forms and android project and using actionbar for navigation style.
So my actionbar theme are like this in style file:

<style name="MyTheme.ActionBarStyle" parent="@android:style/Widget.Holo.Light.ActionBar">
    <item name="android:titleTextStyle">@style/MyTheme.ActionBar.TitleTextStyle</item>
    <item name="android:background">@color/flynnGreen</item>
    <item name="android:windowActionBar">true</item>
    <item name="android:windowNoTitle">false</item>
    <item name ="android:showAsAction">always</item>
  </style>

When I push form main page to sub-pages, I want to show the small 'back' icon like this but my application is only showing the logo but no '<'

I only how it should be working in android only but not sure about forms :

        ActionBar.SetHomeButtonEnabled(true);
        ActionBar.SetDisplayHomeAsUpEnabled(true);

Thanks advanced!