source/php/Parser/EventManagerGroups.php
public function activateNewGroup($termId, $parentId)
    {
        $selectedGroups = get_option('options_event_filter_group', false);
        if (is_array($selectedGroups) && !empty($selectedGroups)) {
            if (in_array($parentId, $selectedGroups)) {
                // Add children to option array
                $selectedGroups[] = (int) $termId;
                update_field('event_filter_group', $selectedGroups, 'option');
            }
        }
    }
public function activateNewGroup($termId, $parentId)
    {
        $selectedGroups = get_option('options_event_filter_group', false);
        if (is_array($selectedGroups) && !empty($selectedGroups)) {
            if (in_array($parentId, $selectedGroups)) {
                // Add children to option array
                $selectedGroups[] = (int) $termId;
                update_field('event_filter_group', $selectedGroups, 'option');
            }
        }
    }
Automatically add new terms to Group filter option if the parent is selected
@param  int $termId Term ID
@param  int $parentId Terms parent ID
@return void