How to extend this function. The task is getLinkedPages must be created and return content depending on the parameter - pdf

Question

How to extend this function. The task is getLinkedPages must be created and return content depending on the parameter.
/**
* Get the contents as a sorted collection tree.
*/
public function getTree(bool $showDrafts = false, bool $renderPages = false, bool $renderLinkedPages = false): Collection
{
$pages = $this->getPages($showDrafts, $renderPages);
$chapters = Chapter::visible()->where('book_id', '=', $this->book->id)->get();
$all = collect()->concat($pages)->concat($chapters);
$chapterMap = $chapters->keyBy('id');
$lonePages = collect();
$pages->groupBy('chapter_id')->each(function ($pages, $chapter_id) use ($chapterMap, &$lonePages) {
$chapter = $chapterMap->get($chapter_id);
if ($chapter) {
$chapter->setAttribute('visible_pages', collect($pages)->sortBy($this->bookChildSortFunc()));[enter image description here][1]
} else {
$lonePages = $lonePages->concat($pages);
}
});
$chapters->whereNull('visible_pages')->each(function (Chapter $chapter) {
$chapter->setAttribute('visible_pages', collect([]));
});
$all->each(function (Entity $entity) use ($renderPages) {
$entity->setRelation('book', $this->book);
if ($renderPages && $entity instanceof Page) {
$entity->html = (new PageContent($entity))->render();
}
});
return collect($chapters)->concat($lonePages)->sortBy($this->bookChildSortFunc());
}