Merge pull request lazychaser#151 from ceesvanegmond/v3

Feature: Decrease number of queries used by nested set

Author: lazychaser

src/Collection.php

@@ -21,7 +21,7 @@ public function linkNodes()
 
         /** @var Node $node */
         foreach ($this->items as $node) {
-            if ( ! isset($node->parent)) {
+            if (! $node->parent_id) {
                 $node->setRelation('parent', null);
             }