Hello,
You can use conditions
{{if isset(\IPS\Output::i()->hiddenElements['nbenhadverts_node_class']) and \IPS\Output::i()->hiddenElements['nbenhadverts_node_class'] == 'IPS\forums\Forum' and $forum = \IPS\Output::i()->hiddenElements['nbenhadverts_node_node']}}
{{ try { $category = \IPS\forums\Forum::load(12345); } catch (\OutOfRangeException $e){} }}
{{if $category and $forum->isChildOf($category)}}
1
{{endif}}
{{endif}}
Change the 12345 on category ID