gistfile1.vb

Function find_or_create_node(dict As Dictionary, key As String) As Dictionary
  If Not dict.Exists(key)
    dict.Add(key, new Dictionary)
  End If
  Return dict.Item(key)
End Function

Sub initialize_or_increment_leaf(dict As Dictionary, key As String, value As Double)
  If Not dict.Exists(key)
    dict.Add(key, value)
  Else
    dict.Item(key) = dict.Item(key) + value
  End If
End Sub

' Use like this
sub_projects_dict = find_or_create_node(projects_dict, project_id);
months_dict = find_or_create_node(sub_projects_dict, sub_project_id);
initialize_or_increment_leaf(months_dict, current_month, working_hours);