Iterate through all pages and output in a single html file - drupal

Question

I need to output a node (ID 2334) including sub-nodes into a single document to print them later.
How can I load all sub-nodes and output them beneath the main node?
Update
I'm using Drupal 8.
I want to combine all subsites for a given node into a single page.
By sub-nodes / sub-sites I'm referring to the navigation tree.
The key goal is to have a printable version of a whole website section.
Like a category where it combines all related articles into one page.
Update 2
I created a custom page controller and managed to get an array of "sub-nodes":
$subnodes = [];
$tree = \Drupal::menuTree()->load('internal', new \Drupal\Core\Menu\MenuTreeParameters());
foreach ($tree as $item) {
if ($item->link->getRouteParameters()['node'] == $node) {
foreach($item->subtree as $subitem) {
$subnodes[] = $subitem->link->getRouteParameters()['node'];
}
}
}
var_dump($subnodes); // array of ids
I'm now wondering how render the given nodes?

Answer 1

I managed to solve it with a custom controller:
public function exportAll($node) {
$node = (int)$node;
if ($node < 1) {
throw new NotFoundHttpException($node . 'not available');
}
$subnodes = [$node];
$tree = \Drupal::menuTree()->load('internal', new \Drupal\Core\Menu\MenuTreeParameters());
foreach ($tree as $item) {
if ($item->link->getRouteParameters()['node'] == $node) {
foreach($item->subtree as $subitem) {
$subnodes[] = $subitem->link->getRouteParameters()['node'];
}
}
}
$nodes = \Drupal\node\Entity\Node::loadMultiple($subnodes);
return $build = \Drupal::entityTypeManager()->getViewBuilder('node')->viewMultiple($nodes);
}