Avalonia/samples/ControlCatalog/MainWindow.xaml

<Window xmlns="https://github.com/avaloniaui" MinWidth="500" MinHeight="300"
        Width="1024" Height="800"
        xmlns:pages="clr-namespace:ControlCatalog.Pages"
        Title="Avalonia Control Gallery"
        Icon="/Assets/test_icon.ico"
        xmlns:local="clr-namespace:ControlCatalog"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:ControlCatalog.ViewModels"
        xmlns:v="clr-namespace:ControlCatalog.Views"
        x:Class="ControlCatalog.MainWindow">

  <NativeMenu.Menu>
    <NativeMenu>
      <NativeMenuItem Header="File">
        <NativeMenuItem.Menu>
          <NativeMenu>
            <NativeMenuItem Header="Open" Clicked="OnOpenClicked"/>
            <NativeMenuItemSeperator/>
            <NativeMenuItem Header="Recent">
              <NativeMenuItem.Menu>
                <NativeMenu/>
              </NativeMenuItem.Menu>
            </NativeMenuItem>
            <NativeMenuItemSeperator/>
            <NativeMenuItem Header="Quit Avalonia" Clicked="OnCloseClicked" Gesture="CMD+Q"/>
          </NativeMenu>
        </NativeMenuItem.Menu>
      </NativeMenuItem>
      <NativeMenuItem Header="Edit">
        <NativeMenuItem.Menu>
          <NativeMenu>
            <NativeMenuItem Header="Copy"/>
            <NativeMenuItem Header="Paste"/>
          </NativeMenu>
        </NativeMenuItem.Menu>
      </NativeMenuItem>
    </NativeMenu>
  </NativeMenu.Menu>

 <Window.DataTemplates>
    <DataTemplate DataType="vm:NotificationViewModel">
      <v:CustomNotificationView />
    </DataTemplate>
  </Window.DataTemplates>
  <DockPanel LastChildFill="True">
    <Menu Name="MainMenu" DockPanel.Dock="Top">
      <MenuItem Header="File">
        <MenuItem Header="Exit" Command="{Binding ExitCommand}" />
      </MenuItem>
      <MenuItem Header="Help">
        <MenuItem Header="About" Command="{Binding AboutCommand}" />
      </MenuItem>
    </Menu>
    <local:MainView />
  </DockPanel>
</Window>