protected function buildNestedArray(array $nodes = [], $parentId = 0)
    {
        $branch = [];

        if (empty($nodes)) {
            $nodes = $this->allNodes();
        }

        foreach ($nodes as $node) {
            if ($node[$this->parentColumn] === $parentId) {
                $children = $this->buildNestedArray($nodes, $node[$this->getKeyName()]);

                if ($children) {
                    $node['children'] = $children;
                }

                $branch[] = $node;
            }
        }

        return $branch;
    }