I had put the following code into sidebar.php to display a list eith sub-categories of “Store” categori and the posts of them.
Hope I understand what you need and it will be helpfull. if not can ask more explicite
<?
// Get categories for parent category store
// Get ID cat by slug
$id_store = get_category_id('store');
$stores = get_categories(array('child_of' => $id_store, 'hide_empty' => 0));
?>
<ul>
<?php foreach ($stores as $categ_list): ?>
<li class="cats-<?php echo $categ_list->cat_ID; ?> dropcats">
<?php echo $categ_list->cat_name; ?>
<?php
$args = array(
'category' => $categ_list->cat_ID,
'numberposts' => -1,
'orderby' => 'title',
'order' => 'asc'
);
// Get posts for store category
$store_posts = get_posts($args);
// If there is any posts
if (count($store_posts) > 0) {
?>
<ul class="markes">
<?php foreach ($store_posts as $post) { ?>
<li class="post-<?php echo $post->ID; ?>">
<a href="https://wordpress.stackexchange.com/questions/26446/<?php echo $post->post_name; ?>" class="marke-<?php echo $post->ID;?>">
<?php echo $post->post_name; ?>
</a>
</li>
<?php } ?>
</li>
</ul>
<?php }
endforeach;
?>
</ul>
</aside>