code: private Region find(Region x) {
      Region current = this.root;
      while (current != NULL_NODE) {
        long res = x.orderRelativeTo(current);
        if (res < 0) {
          current = current.left;
        } else if (res > 0) {
          current = current.right;
        } else {
          return current;
        }
      }
      return null;
    }
docs: Find an item in the tree.
  
  @param x
  the item to search for.
  @return the matching item of null if not found.