diff --git a/src/StackedDag/Base.hs b/src/StackedDag/Base.hs
--- a/src/StackedDag/Base.hs
+++ b/src/StackedDag/Base.hs
@@ -57,6 +57,8 @@
 
 type DepthGroup = M.Map Depth [NodeId]
 
+type NodeDepth = M.Map NodeId Depth
+
 type DepthGroup' = M.Map Depth ([NodeId],[NodeId])
 
 type DepthGroup'' = M.Map Depth ([(NodeId,Cur,Dest)],[(NodeId,Cur,Dest)])
@@ -119,6 +121,10 @@
           (n,d):_ -> (n,sort' $ S.fromList $ map snd a): loop ax
           [] -> loop ax
 
+getNodeDepth :: DepthGroup -> NodeDepth
+getNodeDepth dg = M.fromList $ concat $ map (\(d,nodes) -> map (\node -> (node,d)) nodes) $ M.toList dg
+
+
 pairs edges = do
   (p, c) <- M.toList edges
   child <- S.toList c
@@ -294,6 +300,10 @@
 -- fromList [(0,([3],[])),(1,([2],[])),(2,([1],[0])),(3,([0],[]))]
 -- >>> addBypassNode'' 2 edges (M.fromList [(0,([3],[])),(1,([2],[])),(2,([1],[0])),(3,([0],[]))])
 -- fromList [(0,([3],[])),(1,([2],[0])),(2,([1],[0])),(3,([0],[]))]
+--
+-- >>> edges = mkEdges [(0,[1,2]),(1,[4]),(2,[3]),(3,[4])]
+-- >>> addBypassNode'' 2 edges (M.fromList [(0,([4],[])),(1,([3,1],[])),(2,([2],[0])),(3,([0],[]))])
+-- fromList [(0,([4],[])),(1,([3,1],[])),(2,([2],[0])),(3,([0],[]))]
 addBypassNode'' :: Depth -> Edges -> DepthGroup' -> DepthGroup'
 addBypassNode'' d edges dg | d < 2 = error $ "depth " ++ show d  ++ " must be greater than 2"
                            | otherwise =
@@ -302,10 +312,15 @@
     (Just (nids0,skipnids0),Nothing)        -> dg
     (Nothing,_)                             -> dg
   where
+    nd = getNodeDepth $ getDepthGroup edges
+    getDepth :: NodeId -> Depth
+    getDepth nid = maybe 0 id $ M.lookup nid nd
+    edges' :: Edges
+    edges' = M.fromList $ map (\(n,nids) ->  (n, S.fromList (filter (\nid -> getDepth nid < d) (S.toList nids)))) $ M.toList edges
     elem :: NodeId -> [NodeId] -> Bool
     elem nid nids =
-      case M.lookup nid edges of
-        Just m -> all id (map (\n -> L.elem n nids) (S.toList m))
+      case M.lookup nid edges' of
+        Just m -> all id $ map (\n -> L.elem n nids) $ (S.toList m)
         Nothing -> True
     update :: Depth -> [NodeId] -> DepthGroup' -> NodeId -> DepthGroup'
     update d' nids1 dg' nid0 =
@@ -342,6 +357,10 @@
 -- >>> dg = getDepthGroup edges
 -- >>> addBypassNode edges dg
 -- fromList [(0,([3],[])),(1,([2],[0])),(2,([1],[0])),(3,([0],[]))]
+-- >>> edges = mkEdges [(0,[1,2]),(1,[4]),(2,[3]),(3,[4])]
+-- >>> dg = getDepthGroup edges
+-- >>> addBypassNode edges dg
+-- fromList [(0,([4],[])),(1,([3,1],[])),(2,([2],[0])),(3,([0],[]))]
 addBypassNode :: Edges -> DepthGroup -> DepthGroup'
 addBypassNode edges dg = addBypassNode' edges $ M.fromList $ map (\(k,v)-> (k,(v,[]))) $ M.toList dg
 
diff --git a/stacked-dag.cabal b/stacked-dag.cabal
--- a/stacked-dag.cabal
+++ b/stacked-dag.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 57c444b244471ba568f185b245e319dac1300ef668335859a1516b8b2a0bbe7d
+-- hash: 2188812bea0c0424ece99cd546a16fcd01cedc61c8eacdac83b90c3447583c5d
 
 name:           stacked-dag
-version:        0.1.0.0
+version:        0.1.0.1
 synopsis:       Ascii DAG(Directed acyclic graph) for visualization of dataflow
 description:    Please see the README on GitHub at <https://github.com/junji.hashimoto/stacked-dag#readme>
 category:       Graphs, Graphics