public function getRootNodes()
    {
        $root = [];

        foreach ($this->nodes as $appName => $nodes) {
            foreach ($nodes as $name => $migration) {
                // get the nodes  parent
                $parents = $this->getNodeFamilyTree($appName, $name)->parent;

                // if no parent exist this must be the first migration aka
                // adam/eve which ever tickles your fancy
                if (empty($parents)) {
                    $root[$appName] = $name;
                }
            }
        }

        return $root;
    }