Usage recursive hierarchy tree structure in Linq query with multible tables and return some Json Value

The RecursiveJoin Extension looks pretty nice, but I don't think you need the full power of that code to accomplish your objective. If I understand your question correctly, you need to enumerate over all lists of nodes from root to leaf, dumping each list into a JSON object. To do that, first create the following extension methods:

public static class RecursiveExtensions
{
    public static IEnumerable<TValue> SelfAndParents<TKey, TValue>(this TValue value, IDictionary<TKey, TValue> dictionary, Func<TValue, TKey> getParentKey)
    {
        HashSet<TValue> returned = new HashSet<TValue>();
        do
        {
            yield return value;
            if (!dictionary.TryGetValue(getParentKey(value), out value))
                yield break;
            if (returned.Contains(value))
                throw new InvalidOperationException("Circular reference");
            returned.Add(value);
        }
        while (true);
    }

    public static IEnumerable<List<TValue>> FlattenTree<TKey, TValue>(this IEnumerable<TValue> nodes, Func<TValue, TKey> getKey, Func<TValue, TKey> getParentKey)
    {
        var list = nodes.ToList();                                                          // Don't iterate through the node list more than once.
        var parentKeys = new HashSet<TKey>(list.Select(getParentKey));                      // Built a set of parent keys.
        var dict = list.ToDictionary(getKey);                                               // Build a dictionary of key to value
        var results = list
            .Where(node => !parentKeys.Contains(getKey(node)))                              // Filter out non-leaf nodes
            .Select(node => node.SelfAndParents(dict, getParentKey).Reverse().ToList());    // For each leaf return a list going from root to leaf.
        return results;
    }
}

Then use them as follows:

public static class TestFlatten
{
    public static IEnumerable<FlatData> GetFlatData()
    {
        // Get sample data for testing purposes.
        var list = new List<FlatData>
        {
            new FlatData { Id = 1, ParentId = 0, Text = "Some Root Node" },
            new FlatData { Id = 2, ParentId = 0, Text = "Anadolu Satış Merkezi" },
            new FlatData { Id = 3, ParentId = 2, Text = "Emrullah Çelik" },
            new FlatData { Id = 4, ParentId = 3, Text = "Ahmet İşler" },
            new FlatData { Id = 5, ParentId = 4, Text = "Elpa Pazarlama Nazmi Appak" },
            new FlatData { Id = 6, ParentId = 4, Text = "Elpa Pazarlama Nazmi Appak Redux" },
            new FlatData { Id = 11, ParentId = 1, Text = "Some Child of Some Root Node" },
        };
        return list;
    }

    public static void Test()
    {
        var nodes = GetFlatData();
        var flatNodes = nodes.FlattenTree(d => d.Id, d => d.ParentId);
        var results = flatNodes.Select(
            list => list
                .Select((d, i) => new KeyValuePair<int, FlatData>(i, d))
                .ToDictionary(pair => string.Format("level{0}", pair.Key + 1), pair => pair.Value.Text))
            .ToList();
        var json = JsonConvert.SerializeObject(new { data = results }, Formatting.Indented);
        Debug.WriteLine(json);
    }
}

This produces the JSON output:

{
  "data": [
    {
      "level1": "Anadolu Satış Merkezi",
      "level2": "Emrullah Çelik",
      "level3": "Ahmet İşler",
      "level4": "Elpa Pazarlama Nazmi Appak"
    },
    {
      "level1": "Anadolu Satış Merkezi",
      "level2": "Emrullah Çelik",
      "level3": "Ahmet İşler",
      "level4": "Elpa Pazarlama Nazmi Appak Redux"
    },
    {
      "level1": "Some Root Node",
      "level2": "Some Child of Some Root Node"
    }
  ]
}

Is this what you want? Here I am taking advantage of the fact that Json.NET serializes a dictionary as a JSON object to dynamically create the "levelI" properties as dictionary keys. Also, as you did not define the "val" value, I didn't include it in the dictionary.