How to make my code to tri-state checkbox treeview?

Question

I need to do a tri-state treeview checkbox but so far, I only able to make it to two state which are:

1. if all child checked, parent checked.

2. if partial child checked, parent did not check.

But I wanted to make it if partial child checked, parent show a square check. Here is my JavaScript for my code:

<script type="text/javascript">
$(function () {
    $("[id*=tvPermission] input[type=checkbox]").bind("click", function () {
        var table = $(this).closest("table");
        if (table.next().length > 0 && table.next()[0].tagName == "DIV") {
            //Is Parent CheckBox
            var childDiv = table.next();
            var isChecked = $(this).is(":checked");

            $("input[type=checkbox]", childDiv).each(function () {
                if (isChecked) {
                    $(this).prop("checked", true);
                } else {
                    $(this).prop("checked", false);
                }
            });
        } else {
            //Is Child CheckBox
            var parentDIV = $(this).closest("DIV");

            if ($("input[type=checkbox]", parentDIV).length == $("input[type=checkbox]:checked", parentDIV).length) {
                $("input[type=checkbox]", parentDIV.prev()).prop("checked", true);
            } else {
                $("input[type=checkbox]", parentDIV.prev()).prop("checked", false);
            }
        }
    });
})

How can I modify it to make it tri-state in treeview, because with this code, it shows only two state.

Any better way I can do the tri-state mode?

btw this is my asp.net code for my treeview:

<asp:TreeView ID="tvPermission" runat="server" ShowCheckBoxes="All" NodeWrap="true" NodeIndent="2">

Hope someone can help me. Really appreciate it.

Thanks in advance.