diff --git a/src/FeynmanDiagram.jl b/src/FeynmanDiagram.jl
index 5ed4c1f2..38a410a6 100644
--- a/src/FeynmanDiagram.jl
+++ b/src/FeynmanDiagram.jl
@@ -122,7 +122,7 @@ export multi_product, linear_combination, feynman_diagram, propagator, interacti
 export haschildren, onechild, isleaf, isbranch, ischain, isfactorless, has_zero_subfactors, eldest
 export relabel!, standardize_labels!, replace_subgraph!, merge_linear_combination!, merge_multi_product!, merge_chains!
 export relabel, standardize_labels, replace_subgraph, merge_linear_combination, merge_multi_product, merge_chains
-
+export open_parenthesis, flatten_prod!, flatten_prod
 export optimize!, optimize, merge_all_chains!, merge_all_linear_combinations!, remove_duplicated_leaves!
 
 include("TaylorSeries/TaylorSeries.jl")
diff --git a/src/computational_graph/ComputationalGraph.jl b/src/computational_graph/ComputationalGraph.jl
index 4a50a17f..3979f504 100644
--- a/src/computational_graph/ComputationalGraph.jl
+++ b/src/computational_graph/ComputationalGraph.jl
@@ -50,7 +50,7 @@ export eval!
 include("transform.jl")
 export relabel!, standardize_labels!, replace_subgraph!, merge_linear_combination!, merge_multi_product!, merge_chains!, flatten_chains!
 export relabel, standardize_labels, replace_subgraph, merge_linear_combination, merge_multi_product, merge_chains, flatten_chains
-
+export open_parenthesis, flatten_prod!, flatten_prod
 include("optimize.jl")
 export optimize!, optimize
 
diff --git a/src/computational_graph/transform.jl b/src/computational_graph/transform.jl
index fecf791a..17372852 100644
--- a/src/computational_graph/transform.jl
+++ b/src/computational_graph/transform.jl
@@ -155,6 +155,94 @@ function replace_subgraph(g::AbstractGraph, w::AbstractGraph, m::AbstractGraph)
     return g_new
 end
 
+function open_parenthesis(graph::AbstractGraph)
+    if isempty(graph.subgraphs)
+        return deepcopy(graph)
+    else
+        children = []
+        for sub in graph.subgraphs
+            push!(children, open_parenthesis(sub))
+        end
+        newnode = Graph([]; operator=Sum())
+        if graph.operator == Sum
+            # flatten function make sure that all children are already converted to Sum->Prod two layer graphs, so here when merging the subgraphs we just consider the case when operator are Sum.
+            for (child_idx, child) in enumerate(children)
+                if isempty(child.subgraphs)
+                    push!(newnode.subgraphs, child)
+                    push!(newnode.subgraph_factors, graph.subgraph_factors[child_idx])
+                else
+                    for (grandchild_idx, grandchild) in enumerate(child.subgraphs)
+                        push!(newnode.subgraphs, grandchild)
+                        push!(newnode.subgraph_factors, graph.subgraph_factors[child_idx] * child.subgraph_factors[grandchild_idx])
+                    end
+                end
+            end
+        elseif graph.operator == Prod
+            # When opertaor is Prod, we expand parenthese and replace Prod with a Sum operator.
+            childsub_len = [length(child.subgraphs) for child in children]
+            ordtuple = ((childsub_len[num] > 0) ? (1:childsub_len[num]) : (0:0) for num in eachindex(childsub_len)) #The child with no grand child is labeled with a single idx=0
+            for indices in collect(Iterators.product(ordtuple...)) #Indices for all combination of grandchilds, with one from each child. 
+                newchildnode = Graph([]; operator=Prod())
+                for (child_idx, grandchild_idx) in enumerate(indices)
+                    child = children[child_idx]
+                    if grandchild_idx == 0 #Meaning this node is a leaf node
+                        push!(newchildnode.subgraphs, child)
+                        push!(newchildnode.subgraph_factors, graph.subgraph_factors[child_idx])
+                    else
+                        push!(newchildnode.subgraphs, child.subgraphs[grandchild_idx])
+                        push!(newchildnode.subgraph_factors, graph.subgraph_factors[child_idx] * child.subgraph_factors[grandchild_idx])
+                    end
+                end
+                push!(newnode.subgraphs, newchildnode)
+                push!(newnode.subgraph_factors, 1.0)
+            end
+        end
+        return newnode
+    end
+end
+
+function flatten_prod!(graph::AbstractGraph)
+    if isempty(graph.subgraphs)
+        return graph
+    else
+        children = []
+        for sub in graph.subgraphs
+            push!(children, flatten_prod!(sub))
+        end
+        newchildren = []
+        newfactors = []
+        if graph.operator == Sum
+            for (child_idx, child) in enumerate(children)
+                push!(newchildren, child)
+                push!(newfactors, graph.subgraph_factors[child_idx])
+            end
+        elseif graph.operator == Prod
+            for (child_idx, child) in enumerate(children)
+                if isempty(child.subgraphs) || child.operator == Sum
+                    push!(newchildren, child)
+                    push!(newfactors, graph.subgraph_factors[child_idx])
+                else
+                    for (grandchild_idx, grandchild) in enumerate(child.subgraphs)
+                        push!(newchildren, grandchild)
+                        if grandchild_idx == 1
+                            push!(newfactors, graph.subgraph_factors[child_idx] * child.subgraph_factors[grandchild_idx])
+                        else
+                            push!(newfactors, child.subgraph_factors[grandchild_idx])
+                        end
+                    end
+                end
+            end
+        end
+        graph.subgraphs = newchildren
+        graph.subgraph_factors = newfactors
+        return graph
+    end
+end
+
+function flatten_prod(graph::AbstractGraph)
+    flatten_prod!(deepcopy(graph))
+end
+
 """
     function flatten_chains!(g::AbstractGraph)