static <T> Stream<T> levelOrder(Tree<T> tree) { Stream<T> result = Stream.empty(); final java.util.Queue<Tree<T>> queue = new java.util.LinkedList<>(); queue.add(tree); while (!queue.isEmpty()) { final Tree<T> next = queue.remove(); result = result.prepend(next.getValue()); queue.addAll(next.getChildren().toJavaList()); } return result.reverse(); }