How can I change this line for more subcategories show
<input type="hidden" name="s_category_id" id="category" value="<?php echo $a['s_category_id']; ?>"/>
                      <select id="category_multiple" name="category_multiple" multiple>
                        <?php osc_goto_first_category(); ?>
                        <?php while(osc_has_categories()) { ?>
                          <option value="<?php echo osc_category_id(); ?>" <?php if(in_array(osc_category_id(), $category_array)) { ?>selected="selected"<?php } ?>><?php echo osc_category_name(); ?></option>

                          <?php while(osc_has_subcategories()) { ?>
                            <option value="<?php echo osc_category_id(); ?>" <?php if(in_array(osc_category_id(), $category_array)) { ?>selected="selected"<?php } ?>>-&nbsp;<?php echo osc_category_name(); ?></option>
                          <?php } ?>
                        <?php } ?>
                      </select>

Like tree
category
- subcategory
-- subcategory of subcategory

because in 3rd subcat the attributes dont show

@Zbyszek
Not possible, it is curious that osclass does not have functions for that.
I will take a look on it next week to show all levels.