public function all(PageInterface $current = null)
    {
        $all = new Collection();

        /** @var PageInterface $current */
        $current = $current ?: $this->root();

        if (!$current->root()) {
            $all[$current->path()] = ['slug' => $current->slug()];
        }

        foreach ($current->children() as $next) {
            $all->append($this->all($next));
        }

        return $all;
    }