multivaluedictkeyerror when using AJAX with Django

Question

I have a Django application with the following front-end structure:

Jquery / input.html

<script type="text/javascript">
    $(document).ready(function(){
        var expr1 = {"name":{"key":""}};
        var expr2 = {"name":{"key":""}};
        var childFilter1 = {"filter": {"expr":expr1}};
        var childFilter2 = {"filter": {"expr":expr2}};
        var parentFilter = {"filter": {"func":"AND","leftChild":childFilter1,"rightChild":childFilter2}};
        var childFilter3 = {"filter": {"expr":""}};
        var wholeParentFilter = {"filter": {"func":"OR","leftChild":childFilter3,"rightChild":parentFilter}};

        $.ajax({
            url: "/input/",
            type: "GET",
            data: wholeParentFilter,
            dataType: "json",
            success: function(input_data){
                //alert(input_data);
            }
        });
    })
</script>

Django / views.py:

def input(request):
    data = request.GET["filter"]        
    print data

    return HttpResponse(json.dumps("ABC"))

When I try to get JSON value with request.GET["filter"], Django returns the following error and no data print out:

   data = request.GET["filter"]
File "C:\Python27\lib\site-package\django-1.6.2-py2.7.egg\django\utils\datastrucutre.py", line 301, in __getitem__
   raise MultiValueDictKeyError(repr(key))
MultiValueDictKeyError: "'filter'"

I want to use "filter" as tree because it may include sub-filter, so I don't want to change name of "filter" in JSON, any idea for transferring data from front to end? Thanks a lot.

---

UPDATE

Problem is caused by wholdPatrentFilter without transferred into JSON object, add $.toJSON could solve it.

        $.ajax({
            url: "/input/",
            type: "GET",
            data: $.toJSON(wholeParentFilter),
            dataType: "json",
            success: function(input_data){
                //alert(input_data);
            }
        });

Thanks a lot @alecxe for your help.