Why is my MasterDetailPage not showing a menu/burger icon in IOS, but does in Android?

I have a simple view in the app which has a master detail page with a menu page and a content page (the content isn't relevant):

public class MainApp : Application
{
    public MainApp()
    {
        MainPage = new MasterPage();
}

}

public class MasterPage : Xamarin.Forms.MasterDetailPage
{
    public MasterPage()
    {
        this.Title = "";
        Detail = new NavigationPage(new AContentPage()) { BarBackgroundColor = Color.FromHex("e95a0c"), BarTextColor = Color.White, BackgroundColor = Color.White };
    }
}

But the 3 lines icon doesn't appear. It does in Android, but in IOS it's not there - however you can still tap on it to open up the menu.

Any idea?