<MenuItem x:Name="CustomMenuItem"
         Command="{Binding Path=Command, Mode=OneWay}">
   <MenuItem.Header>
        <ContentPresenter x:Name="MenuContentControl"
                          Content="{Binding Path=Content, Mode=OneWay}"/>
   </MenuItem.Header>
</MenuItem>

<MenuItem Header="submenuitem1"
          StaysOpenOnClick="true"
          IsCheckable="true"/>