TreeNode.java

public class TreeNode {
  private final String name;
  private final Collection<TreeNode> children;

  public TreeNode(String name) {
    this.name = name;
    children = new HashSet<TreeNode>();
  }

  public String getName() {
    return this.name;
  }

  public Collection<TreeNode> getChildren() {
    // don't show your privates!
    return Collections.unmodifiableCollection(children);
  }

  public void addChild(final TreeNode treeNode) {
    children.add(treeNode);
  }
}