Cannot open the secondary menu of ribbon:Menu

<Window x:Class="WpfApp11.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:ribbon="http://schemas.actiprosoftware.com/winfx/xaml/ribbon"
        xmlns:local="clr-namespace:WpfApp11"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <ribbon:Menu>
            <MenuItem Header="Test">
                <Label>123</Label>
            </MenuItem>
        </ribbon:Menu>
    </Grid>
</Window>

Click on the'MenuItem' in this code'Menu' cannot be expanded