code: public Node getNode(int index)
      {
          if (index == 0)
          {
              return this;
          }
          int leftNodes = left.countNodes();
          if (index <= leftNodes)
          {
              return left.getNode(index - 1);
          }
          else
          {
              return right.getNode(index - leftNodes - 1);
          }
      }
docs: {@inheritDoc}