private void serializeNode(Node<T> node, List<T> list, int level) {
        node.data().treeLevel(level);
        list.add(node.data());
        node.forEach(n -> serializeNode(n, list, level + 1));
    }
@author Nico Bergemann <barracuda415 at yahoo.de>
disunity-core/src/main/java/info/ata4/junity/serialize/typetree/TypeTreeV3.java