@Override
    public void remove() {
      throw new UnsupportedOperationException();
    }
Create the iterator starting from the specified key
@param root          the current root of the tree
@param key           the key for the node we are trying to find
@param keyComparator the comparator to use to match node and key
hbase-common/src/main/java/org/apache/hadoop/hbase/util/AvlUtil.java