Change

<input id="dropdowntree"/>

<script>
$("#dropdowntree").kendoDropDownTree({
  dataSource: [{ text: "item1", value: 1 }, { text: "item2", value: 2 }],
  change: function(e) {
    var value = this.value();
    // Use the value of the widget
  }
});
</script>

<input id="dropdowntree"/>

<script>
function dropdowntree_change(e) {
  var value = this.value();
  // Use the value of the widget
}
$("#dropdowntree").kendoDropDownTree();
var dropdowntree = $("#dropdowntree").data("kendoDropDownTree");
dropdowntree.bind("change", dropdowntree_change);
</script>