<NavigationView x:Name="nvSample"
                MenuItemTemplateSelector="{StaticResource selector}"
                MenuItemsSource="{x:Bind Categories, Mode=OneWay}" />

<local:MenuItemTemplateSelector x:Key="selector">
    <local:MenuItemTemplateSelector.ItemTemplate>
        <DataTemplate x:DataType="local:Category" >
            <NavigationViewItem Content="{x:Bind Name}" ToolTipService.ToolTip="{x:Bind Tooltip}">
                <NavigationViewItem.Icon>
                    <SymbolIcon Symbol="{x:Bind Glyph}" />
                </NavigationViewItem.Icon>
            </NavigationViewItem>
        </DataTemplate>
    </local:MenuItemTemplateSelector.ItemTemplate >
</local:MenuItemTemplateSelector>

//C# code behind
Categories = new ObservableCollection<CategoryBase>();
Categories.Add(new Category { Name = "Category 1", Glyph = Symbol.Home, Tooltip = "This is category 1" });
Categories.Add(new Category { Name = "Category 2", Glyph = Symbol.Keyboard, Tooltip = "This is category 2" });
Categories.Add(new Category { Name = "Category 3", Glyph = Symbol.Library, Tooltip = "This is category 3" });
Categories.Add(new Category { Name = "Category 4", Glyph = Symbol.Mail, Tooltip = "This is category 4" });

public class CategoryBase { }

public class Category : CategoryBase
{
    public string Name { get; set; }
    public string Tooltip { get; set; }
    public Symbol Glyph { get; set; }
}

public class Separator : CategoryBase { }

public class Header : CategoryBase
{
    public string Name { get; set; }
}

[ContentProperty(Name = "ItemTemplate")]
class MenuItemTemplateSelector : DataTemplateSelector
{
    public DataTemplate ItemTemplate { get; set; }
    protected override DataTemplate SelectTemplateCore(object item)
    {
        return item is Separator ? SeparatorTemplate : item is Header ? HeaderTemplate : ItemTemplate;
    }
}