Different menu items can be added to an application menu using the MenuItems property of the ApplicationMenu class. Kindly make use of the code snippet to add the menu items in application menu.

[XAML]
<syncfusion:Ribbon Name="MyRibbon">
<!--Applicaton Menu-->
<syncfusion:Ribbon.ApplicationMenu>
<syncfusion:ApplicationMenu>
<syncfusion:ApplicationMenu.MenuItems>
<TextBlock MinWidth="300" FontWeight="Bold">Create New Outlook Item</TextBlock>
<Separator Padding="0"/>
</syncfusion:ApplicationMenu.MenuItems>
<!--Footer items-->
<syncfusion:ApplicationMenu.ApplicationItems>
<syncfusion:ButtonPanel>
<syncfusion:RibbonButton SizeForm = "Small" Label="Edit Options" />
</syncfusion:ButtonPanel>
</syncfusion:ApplicationMenu.ApplicationItems>
</syncfusion:ApplicationMenu>
</syncfusion:Ribbon.ApplicationMenu>
</syncfusion:Ribbon>