Category menu item and its last 10 posts as sub-menu

I finally achieve it with this code in function.php

// Front end only, don't hack on the settings page
if ( ! is_admin() ) {
// Hook in early to modify the menu
// This is before the CSS "selected" classes are calculated
add_filter( 'wp_get_nav_menu_items', 'display_lasts_ten_posts_for_categories_menu_item', 10, 3 );
}

// Add the ten last posts of af categroy menu item in a sub menu
function display_lasts_ten_posts_for_categories_menu_item( $items, $menu, $args ) {


$menu_order = count($items); /* Offset menu order */
$child_items = array();

// Loop through the menu items looking category menu object
foreach ( $items as $item ) {

    // Test if menu item is a categroy and has no sub-category
    if ( 'category' != $item->object || ('category' == $item->object && get_category_children($item->object_id)) )
        continue;

    // Query the lasts ten category posts
    $category_ten_last_posts = array(
            'numberposts' => 10,
            'cat' => $item->object_id,
            'orderby' => 'date',
            'order' => 'DESC'
    );

    foreach ( get_posts( $category_ten_last_posts ) as $post ) {
        // Add sub menu item
        $post->menu_item_parent = $item->ID;
        $post->post_type="nav_menu_item";
        $post->object="custom";
        $post->type="custom";
        $post->menu_order = ++$menu_order;
        $post->title = $post->post_title;
        $post->url = get_permalink( $post->ID );
        /* add children */
        $child_items[]= $post;
    }
}
return array_merge( $items, $child_items );
}

This will display as sub menu, the ten last posts of a category placed as menu item or sub menu item in admin panel.

This code is highly inspired from this: http://codeseekah.com/2012/03/05/list-all-posts-in-wordpress-navigation-menu/