jQuery Grid Plugin - jqGrid

I hope you can help me, I have a structure like this:

- root A
    -child_A1
        -child_A1_1
        -child_A1_2
        -child_A1_3
    -child_A2
        -child_A2_1
        -child_A2_2
        -child_A2_3

- root B
    - child_B1
         -child_B1_1
         -child_B1_2
         -child_B1_3

But when I show the data in TreeGrid, it shows like this:

- root A
    -child_A1

    -child_A2
         -child_A1_1

- root B
    - child_B1
         -child_B1_1
         -child_B1_2
         -child_B1_3
         -child_A1_2
         -child_A1_3
         -child_A2_1
         -child_A2_2
         -child_A2_3

Anybody knows why..??? please help, I search information about this error but don`t have luck...

here the code of my json string:

{"total":1,"page":null,"records":18,"rows":[
      {"cell":["Parent A","ubicacion","0","null","false","false","true"]},
      {"cell":["Child A1","ubicacion","1","1","false","false","true"]},
      {"cell":["Child A2","ubicacion","1","1","false","false","true"]},
      {"cell":["Child A1_1","ubicacion","2","2","true","false","true"]},
      {"cell":["Parent B","ubicacion","0","null","false","false","true"]},
      {"cell":["Child B1","ubicacion","1","5","false","false","true"]},
      {"cell":["Child B1_1","ubicacion","2","6","true","false","true"]},
      {"cell":["Child B1_2","ubicacion","2","6","true","false","true"]},
      {"cell":["Child B1_3","ubicacion","2","6","true","false","true"]},
      {"cell":["Child A1_2","ubicacion","2","2","true","false","true"]},
      {"cell":["Child_A1_3","ubicacion","2","2","true","false","true"]},
      {"cell":["Child A2_1","ubicacion","2","3","true","false","true"]},
      {"cell":["Child A2_2","ubicacion","2","3","true","false","true"]},
      {"cell":["Child A2_3","ubicacion","2","3","true","false","true"]}
    ]}

I hope anybody can help me, thanks in advance...

Best Regards,

Verónica.