Knockout custom binding not triggering for Update to observable
<p>I have a simple binding test. The Init and Update are called when the page opens. But if I manually update the objervable by calling a function to do it the update method is not being called in my binding handler.</p>

<p>SO it starts with selectedQueue being set to 2. Clicking the button correctly selects the 3rd element in the select. But my binding handler is not being called for this change.</p>

<p>Is there something simple I am missing?</p>

<pre><code>    &lt;select id="productGroup" name="productGroupen" data-bind="value:selectedQueue, treeMenu: selectedQueue"&gt;
    &lt;option value="1" selected="selected"&gt;Group 1&lt;/option&gt;
    &lt;option value="2"&gt;Group 2&lt;/option&gt;
    &lt;option value="3"&gt;Group 3&lt;/option&gt;
&lt;/select&gt;

&lt;div data-bind="text: selectedQueue"&gt;&lt;/div&gt;

&lt;button data-bind="click:setQueue"&gt;Set to 3&lt;/button&gt;

    &lt;script src="~/Scripts/knockout-3.4.0.js"&gt;&lt;/script&gt;

    &lt;script&gt;

        ko.bindingHandlers.treeMenu = {
            init: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
                alert("init")
                x = valueAccessor();
            },
            update: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
                alert("update");
                x = valueAccessor();
            }
        };


        var Model = function () {
            self = this;

            this.selectedQueue = ko.observable(2);
            this.setQueue = function () {
                this.selectedQueue(3);

            }

        }
        $(document).ready(function () {
            ko.applyBindings(new Model());
        });


    &lt;/script&gt;
</code></pre>