WPF Menu MenuItem default ItemsPanel ItemsPanelTemplate

<Window x:Class="WpfApp399.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp399"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Menu>            
            <MenuItem Header="_File">
                <MenuItem Header="_New..."/>
                <MenuItem Header="_Open..."/>
                <Separator/>
                <MenuItem Header="Send To">
                    <MenuItem Header="Mail Recipient"/>
                    <MenuItem Header="My Documents"/>
                </MenuItem>
            </MenuItem>
            <MenuItem Header="_Edit">
                <MenuItem Header="_Edit File"/>
                <Separator/>
                <MenuItem Header="_Edit Folder"/>
            </MenuItem>
            <MenuItem Header="_View">
                <MenuItem Header="_View_File"/>
                <Separator/>
                <MenuItem Header="_View_Folder"/>
            </MenuItem>
        </Menu>
    </Grid>
</Window>