[
    [{
        "timestamp": 1324374926
    }],
    [{
        "id": "9",
        "neme": "qqq"
    }, {
        "id": "19",
        "neme": "qqq"

    }, {
        "id": "29",
        "neme": "qqq"
    }]
]

DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(Categor[]));
 Categor[] result = (Categor[])serializer.ReadObject(responseStream);

DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(Categor[]));
 Categor[] result = (Categor[])serializer.ReadObject(responseStream);
[

{
    "category": "A",
    "subcategories": [
        {
            "id": "QW",
            "name": "A",
            "ranking": 100,
            "isVisible": true
        },
        {
            "id": "QWN0d",
            "name": "Pol",
            "ranking": 101,
            "isVisible": false
        },

[DataContract]
    public class Articlesubcat
    {
        [DataMember(Name = "id")]
        public string id { get; set; }
        [DataMember(Name = "name")]
        public string name { get; set; }
        [DataMember(Name = "ranking")]
        public string ranking { get; set; }
        [DataMember(Name = "isVisible")]
        public string isVisible { get; set; }

    }

    [DataContract]
    public class Categor
    {
           [DataMember(Name = "category")]
        public string category { get; set; }
            [DataMember(Name = "subcategories")]
        public List<Articlesubcat> subcat { get; set; }
    }

[
[
 {
    "timestamp": 1324374926
 }
],
[
  {
    "id": "9",
    "neme": "qqq"
  },
  {
    "id": "19",
    "neme": "qqq"

   },
   {
    "id": "29",
    "neme": "qqq"
   }
 ]
]