anchor.diff:      {{_LeastMbr, LeastPos}, LeastRest} = least_expansion(
               Fd, SubtreeMbr, EntriesPos),
       LeastRestPos = [Pos || {Mbr, Pos} <- LeastRest],
  +?debugVal(length(LeastRestPos)),
       case insert_subtree(Fd, LeastPos, Subtree, Level, Depth+1) of
       {ok, NewMbr, NewPos, Inc} ->
           MergedMbr = vtree:merge_mbr(ParentMbr, NewMbr),
  +?debugVal(length([NewPos|LeastRestPos])),
           NewNode = {MergedMbr, #node{type=inner}, [NewPos|LeastRestPos]},
           {ok, Pos} = couch_file:append_term(Fd, NewNode),
           {ok, NewMbr, Pos, Inc};
  
positive.code:     %insert_subtree(Fd, RootPos, Subtree, Level, 0),
      case insert_subtree(Fd, RootPos, Subtree, Level, 0) of
      {splitted, NodeMbr, {Node1Mbr, NodePos1}, {Node2Mbr, NodePos2}, Inc} ->
          Parent = {NodeMbr, #node{type=inner}, [NodePos1, NodePos2]},
          {ok, Pos} = couch_file:append_term(Fd, Parent),
          {ok, NodeMbr, Pos, Inc+1};
      {ok, NewMbr, NewPos, Inc} ->
          {ok, NewMbr, NewPos, Inc}
      end.
  
  
negative.code:     Diff when Diff > 0 ->
      ?debugMsg("target tree higher"),
          {ok, _, SubPos, Inc} = insert_subtree(Fd, TargetPos, MbrAndPosList, Diff-1),
  ?debugVal(SubPos),
          {SubPos, TargetHeight+Inc};
      % insert target tree into new tree
      Diff when Diff < 0 ->
  