[0]            ng1
  [1][0]          ng1_1
   [1][1][0]        ng1_1_1
    [1][1][1][0]     ng1_1_1_u1
    [1][1][1][1]     ng1_1_1_u2
    [1][1][1][2]     ng1_1_1_u3
   [1][1][2]        ng1_1_2
   [1][1][3]        ng1_1_3
   [1][1][4]        ng1_1_4
  [1][2]          ng1_2
  [1][3]          ng1_3
  [1][4]          ng1_4
 [2]            ng2
  [3][0]          ng2_1
   [3][1][0]       ng2_1_u1
   [3][1][1]       ng2_1_u2
   [3][1][2]       ng2_1_u3
  [3][2]          ng2_2
  [3][3]          ng2_3
  [3][4]          ng2_4
 [4]            ng3
  [5][0]          ng3_1
  [5][1]          ng3_2
  [5][2]          ng3_3
  [5][3]          ng3_4