null created by anonymous - https://repl.it/KYkY/1

KYkY-1.java

import java.util.*;

public class Main {
  private static class Node {
    public final char value;
    public final Node left;
    public final Node right;

    public Node(char value, Node left, Node right) {
      this.value = value;
      this.left = left;
      this.right = right;
    }
  }

  /**
   * -------A--------
   * -----/--\-------
   * ----U----D------
   * --/--\----\-----
   * -I----B----L----
   * -----/----------
   * ----E-----------
   */
  private static final Node TREE = new Node(
      'A', new Node('U', new Node('I', null, null), new Node('B', new Node('E', null, null), null)), new Node('D', null, new Node('L', null, null))
  );

  private static void printTree(Node root) {
    final List<Node> all = new ArrayList<Node>();
    for (List<Node> children = Collections.singletonList(root); children.size() > 0; children = getDirectChildren(children)) {
      all.addAll(children);
    }
    for (Node n : all) {
      System.out.print(n.value);
    }
    System.out.println();
  }

  private static List<Node> getDirectChildren(List<Node> nodes) {
    final List<Node> children = new ArrayList<Node>();
    for (Node child : nodes) {
      if (null != child.left) children.add(child.left);
      if (null != child.right) children.add(child.right);
    }
    return children;
  }

  private static void printTreeWithQueue(Node root) {
    final Queue<Node> queue = new LinkedList<Node>();
    queue.add(root);
    while (!queue.isEmpty()) {
      final Node next = queue.remove();
      System.out.print(next.value);
      if (next.left != null) queue.add(next.left);
      if (next.right != null) queue.add(next.right);
    }
    System.out.println();
  }

  public static void main(String[] args) {
    System.out.println("List:");
    printTree(TREE);
    System.out.println("Queue:");
    printTreeWithQueue(TREE);
  }
}