Hide subcategories (widget)

Greetings,

So I am working on making a widget, I have the option to hide categories from it. The list with options of what to hide consist of both categories and subcategories. Now, the problem is, if I tick a main category then all subcategories will automatically be shown also. Meaning nothing will be hidden. If I only tick subcategories without its parent, well then everything will be shown on the page as long as its parent is ticked. Any ideas on how I can enable hiding subcategories while showing its parent?

<p>
			<label for="<?php echo $this->get_field_id('nr_rows'); ?>"><?php _e('Only show cities below'); ?>:</label>
			<?php echo '<input type="checkbox" name="'.$this->get_field_name('only_these').'"  value="1" '.(
	 $instance['only_these'] == "1" ? ' checked="checked" ' : "" ).' /> '; ?>
		</p>

        <p>
			<label for="<?php echo $this->get_field_id('nr_rows'); ?>"><?php _e('Cities to show'); ?>:</label>

                <div style=" width:220px;
    height:180px;
    background-color:#ffffff;
    overflow:auto;border:1px solid #ccc">
     <?php

	 $terms = get_terms("ad_city","ad_city=0&hide_empty=0");
	 foreach ( $terms as $term ) {

	 echo '<input type="checkbox" name="'.$this->get_field_name('term_'.$term->term_id).'"  value="'.$term->term_id.'" '.(
	 $instance['term_'.$term->term_id] == $term->term_id ? ' checked="checked" ' : "" ).' /> ';
	 echo $term->name.'<br/>';

Any help would be much appreciated 🙂