final List<Tree> children;

    public Tree(char value, Tree... children) {
      super(value);
      this.children = Arrays.asList(children);
    }
  }

  private static final TreeTraverser<Tree> ADAPTER =
      new TreeTraverser<Tree>() {
        @Override
        public Iterable<Tree> children(Tree node) {
          return node.children;
        }
      };

    final List<Tree> children;

    public Tree(char value, Tree... children) {
      super(value);
      this.children = Arrays.asList(children);
    }
  }

  private static final TreeTraverser<Tree> ADAPTER =
      new TreeTraverser<Tree>() {
        @Override
        public Iterable<Tree> children(Tree node) {
          return node.children;
        }
      };