If you’re comfortable doing so, locate the file mdocs-functions.php
On line 577-581 you’ll find the following block of code
<tr class="mdocs-current-cat" >
<td colspan="<?php echo $num_cols; ?>" id="title" class="mdocs-tooltip">
<p><i class="fa fa fa-folder-open-o"></i> <?php echo $current_cat['name']; ?></p>
</td>
</tr>
If you move that block to line 563 (before the php tag, which should move down to line 568) I think you’ll get something closer to what you’re looking for. The “Main” folder will appear as a title at the top of the list but only when it too has a parent.
Note that this modification will likely get overwritten if/when the plug in is updated.
PS I’m a PHP coder but a WP newbie – if suggesting someone modify a file is a no-no, just ignore everything above this line.
