Wrap description and sub menu in a wrapper

I am trying to add a wrapper to description and sub-menu in wordpress using walker class, Description will only be shown for the first menu so the structure will look like this

EDIT

I have been able to add a wrapper div to description but not to sub-menu and menu description together so I am seeking assistance with adding a wrapper div to menu description and sub-menu(if any)

ul id="menu-main-menu" class="primary-nav"
    li id="menu-item-41" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-has-children first"
        a href="http://link" class="menu-image-title-after menu-image-not-hovered"Menu 1/a
        div class='MainMenuWrapper' !--   NEW WRAPPER STARTS  ---
            ul class="nav_desc"li class="first"img src="http://link/arrow.png"/lili class="last"Menu description Goes here./li/ul
            ul class="sub-menu"
            li id="menu-item-44" class="menu-item menu-item-type-post_type menu-item-object-page first"a href="http://link" class="menu-image-title-after menu-image-not-hovered"img width="84" height="46" src="http://link/sub_menu_bg1.png" class="menu-image menu-image-title-after" alt="Image Kitchen"Kitchen/a/li
            /ul
        /div    !--   NEW WRAPPER ENDS  ---
    /li
/ul

This is the code I am currently using

class Description_Walker extends Walker_Nav_Menu
{
public function start_el( $output, $item, $depth = 0, $args = array(), $id = 0 )
    {
        $classes     = empty ( $item-classes ) ? array () : (array) $item-classes;

        $class_names = join(
            ' '
        ,   apply_filters(
                'nav_menu_css_class'
            ,   array_filter( $classes ), $item
            )
        );

        ! empty ( $class_names )
            and $class_names = ' class="'. esc_attr( $class_names ) . '"';

        $output .= "li id='menu-item-$item-ID' $class_names";

        $attributes  = '';

        ! empty( $item-attr_title )
            and $attributes .= ' title="'  . esc_attr( $item-attr_title ) .'"';
        ! empty( $item-target )
            and $attributes .= ' target="' . esc_attr( $item-target     ) .'"';
        ! empty( $item-xfn )
            and $attributes .= ' rel="'    . esc_attr( $item-xfn        ) .'"';
        ! empty( $item-url )
            and $attributes .= ' href="'   . esc_attr( $item-url        ) .'"';

        // insert description for top level elements only
        // you may change this

        $description = ( ! empty ( $item-description ) and 0==$depth  )
            ? 'ul class="nav_desc"liimg src="'.get_bloginfo( 'template_url' ).'/images/arrow.png"/lili' . esc_attr( $item-description ) . '/li/ul' : '';

            // $description = ( ! empty ( $item-description )  )
            // ? 'span class="nav_desc"' . esc_attr( $item-description ) . '/span' : '';

        $title = apply_filters( 'the_title', $item-title, $item-ID );

        $item_output = $args-before
            . "a $attributes"
            . $args-link_before
            . $title
            . '/a '
            . $args-link_after
            . $description
            . $args-after;

        // Since $output is called by reference we don't need to return anything.
        $output .= apply_filters(
            'walker_nav_menu_start_el'
        ,   $item_output
        ,   $item
        ,   $depth
        ,   $args
        );
    }
}