private void traverse(WordNode k, StringBuilder str) {
    if (k == null) {
      return;
    }
    for (int i = 0; i < 26; i++) {
      if (k.subNodes[i] != null) {
        str = str.append(k.letter);
        if (k.subNodes[i].count > 0) {
          this.xml = this.xml + "<"+str.toString()+"><"+k.subNodes[i].count+">\n";
        }
        traverse(k.subNodes[i],str);
      }
    }
  }