Tree create infinite child element.

Please see the attach file
I applied code from demo.
May be something wrong in json file.
Could you please advice?
Thank you.
<body>
<h2>CheckBox Tree</h2>
<p>Tree nodes with check boxes.</p>
<div style="margin:20px 0;">
<a href="#" class="easyui-linkbutton" onclick="getChecked()">GetChecked</a>
</div>
<div style="margin:10px 0">
<input type="checkbox" checked onchange="$('#tt').tree({cascadeCheck:$(this).is(':checked')})">CascadeCheck
<input type="checkbox" onchange="$('#tt').tree({onlyLeafCheck:$(this).is(':checked')})">OnlyLeafCheck
</div>
<div class="easyui-panel" style="padding:5px">
<ul id="tt" class="easyui-tree" data-options="url:'treedata3.json',method:'get',animate:true,checkbox:true"></ul>
</div>
<script type="text/javascript">
function getChecked(){
var nodes = $('#tt').tree('getChecked',['checked','indeterminate']);
console.log(nodes);
var s = '';
for(var i=0; i<nodes.length; i++){
if (s != '') s += ',';
s += nodes[i].id;
}
alert(s);
}
</script>
</body>