how do I collpase and expand all tree nodes in a Kendo UI treeView based on a button click?

This is not working:

<script type="text/javascript">
            $('#btnCollapseAll').click(function()
            {
                $('#treeview').collapseAll();
            });
</script>

You can use this code

1: collapse

collapse kendoTreeView document

    $("#treeview").kendoTreeView();
            var treeview = $("#treeview").data("kendoTreeView");
            treeview.collapse(document.getElementById("firstItem"));
            $('#btn').click(function () {
                // collapse the node with id="firstItem"

                // collapse all nodes
                treeview.collapse(".k-item");
            });

2:expand

expand kendoTreeView document

 $("#treeview").kendoTreeView();
        var treeview = $("#treeview").data("kendoTreeView");
        treeview.collapse(document.getElementById("firstItem"));
        $('#btn').click(function () {
            // expand the node with id="firstItem"

            // expand all nodes
            treeview.expand(".k-item");
        });