jstree - how to use method get_top_selected

jstree - how to use method get_top_selected

Hello jsquery users
I am trying to use jstree plugin. The tree is viewed perfectly and the leafes are perfectly selectable.
I want to push a button and then get displayed the selected nodes.
I looked up many proposals and tutorial but could not yet solve the issue.
 
my html form looks like:
  1. <form id="suchphrase" name="suchphrase" method="post">
    <button id="summary" class="btn">Summary</button>
    </form>

  2. <div id="jstree_demo_div"></div>
my js is as: Can you help me with this?, Thanks for assistance, Peter
  1. $("#summary").click(function() {
    $("#jstree_demo_div").bind("click.jstree", function (event) {
        alert($(event.currentTarget).parent("li:first").text().trim());
    }); return false; });