Sub Menu Item Command MVVM

Question

<MenuItem Header="Flag(s)" ItemsSource="{Binding Path=LineItemFlags}" Command="{Binding AssignFollowupCommand}">
    <MenuItem.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding FlagName}">    
            </TextBlock>
        </DataTemplate>
    </MenuItem.ItemTemplate>
</MenuItem>

For the parent Item i mean menu item i have a command it's invoking i want to know how to setup command for Sub Menu item