tv.Attributes.Add(onclick, OnTreeClick(event));

Add this javascript code

<script language=javascript type=text/javascript>

    function OnTreeClick(evt) {

        var src = window.event != window.undefined ? window.event.srcElement : evt.target;

        var isChkBoxClick = (src.tagName.toLowerCase() == input && src.type == checkbox);

        if (isChkBoxClick) {

            var parentTable = GetParentByTagName(table, src);

            var nxtSibling = parentTable.nextSibling;

            if (nxtSibling && nxtSibling.nodeType == 1)//check if nxt sibling is not null & is an element node

            {

                if (nxtSibling.tagName.toLowerCase() == div) //if node has children

                {

                    //check or uncheck children at all levels

                    CheckUncheckChildren(parentTable.nextSibling, src.checked);

                }

            }

            //check or uncheck parents at all levels

            CheckUncheckParents(src, src.checked);

        }

    }



    function CheckUncheckChildren(childContainer, check) {

        var childChkBoxes = childContainer.getElementsByTagName(input);

        var childChkBoxCount = childChkBoxes.length;

        for (var i = 0; i < childChkBoxCount; i++) {

            childChkBoxes[i].checked = check;

        }

    }



    function CheckUncheckParents(srcChild, check) {

        var parentDiv = GetParentByTagName(div, srcChild);

        var parentNodeTable = parentDiv.previousSibling;



        if (parentNodeTable) {

            var checkUncheckSwitch;



            if (check) //checkbox checked

            {

                var isAllSiblingsChecked = AreAllSiblingsChecked(srcChild);

                if (isAllSiblingsChecked)

                    checkUncheckSwitch = true;

                else

                    return; //do not need to check parent if any(one or more) child not checked

            }

            else //checkbox unchecked

            {

                checkUncheckSwitch = false;

            }



            var inpElemsInParentTable = parentNodeTable.getElementsByTagName(input);

            if (inpElemsInParentTable.length > 0) {

                var parentNodeChkBox = inpElemsInParentTable[0];

                parentNodeChkBox.checked = checkUncheckSwitch;

                //do the same recursively

                CheckUncheckParents(parentNodeChkBox, checkUncheckSwitch);

            }

        }

    }



    function AreAllSiblingsChecked(chkBox) {

        var parentDiv = GetParentByTagName(div, chkBox);

        var childCount = parentDiv.childNodes.length;

        for (var i = 0; i < childCount; i++) {

            if (parentDiv.childNodes[i].nodeType == 1) //check if the child node is an element node

            {

                if (parentDiv.childNodes[i].tagName.toLowerCase() == table) {

                    var prevChkBox = parentDiv.childNodes[i].getElementsByTagName(input)[0];

                    //if any of sibling nodes are not checked, return false

                    if (!prevChkBox.checked) {

                        return false;

                    }

                }

            }

        }

        return true;

    }



    //utility function to get the container of an element by tagname

    function GetParentByTagName(parentTagName, childElementObj) {

        var parent = childElementObj.parentNode;

        while (parent.tagName.toLowerCase() != parentTagName.toLowerCase()) {

            parent = parent.parentNode;

        }

        return parent;

    }



</script>