code: public static <K, V> OMVRBTreeEntry<K, V> previous(final OMVRBTreeEntry<K, V> t) {
      if (t == null)
        return null;
  
      final int index = t.getTree().getPageIndex();
  
      final OMVRBTreeEntry<K, V> prev;
      if (index <= 0) {
        prev = predecessor(t);
        if (prev != null)
          t.tree.pageIndex = prev.getSize() - 1;
        else
          t.tree.pageIndex = 0;
      } else {
        prev = t;
        t.tree.pageIndex = index - 1;
      }
  
      return prev;
    }
docs: Returns the previous item of the tree.