@Override
    public boolean removeAll(Collection<?> c) {
        List<Node<T>> childrenOld = new ArrayList<>(children);
        boolean removed = children.removeAll(c);
        if (removed) {
            childrenOld.removeAll(children);
            childrenOld.forEach(node -> node.parent(null));
        }
        return removed;
    }
@author Nico Bergemann <barracuda415 at yahoo.de>
@param <T>
disunity-core/src/main/java/info/ata4/util/collection/Node.java