I am facing problem in rerendering the treepanel when I select value from selectlist.The jsonstring in the controller is right but it is not reflecting in jstree.

Below is the code. Please help on how to fix this.
 

<apex:page controller="customcontroller" sidebar="false" id="page">

        <apex:includeScript value="{!$Resource.jquerymin}"/>
        <apex:stylesheet value="{!URLFOR($Resource.jstree, '/jstree/dist/themes/default/style.min.css')}"/>
        <script src="{!URLFOR($Resource.jstree, '/jstree/dist/jstree.min.js')}"></script>
        <apex:stylesheet value="{!$Resource.AlignmaxCommonCSS}"/>
        <script>
        $( document ).ready(function() {
            createTree();
        });
            function createTree(){
                var j$=jQuery.noConflict();
                j$(function(){
                j$('#jstree').jstree({

                        "core" : {
                        "check_callback" : true,
                        "themes" : { "stripes" : true },        
                        'data' : {!jsonString}

                        }
                   }); 

                });
                alert('inside tree Json String'+JSON.stringify({!jsonString}));
            }
        </script>
        <apex:form id="form">
          <div class="box-main">


            <div class="box-content">
                <apex:actionStatus startText=" (Shant Baitho...!!!)" stopText="" id="processingStatus" />
                <apex:actionFunction name="TreeRefresh"   status="processingStatus" action="{!processTeam}"  />
                <apex:selectList value="{!selectedTeam}" size="1" style="width:20%;" onchange="TreeRefresh();" >
                    <apex:selectOptions value="{!TeamList}"></apex:selectOptions>
                </apex:selectList>
                <div class="tree">
                    Tree Structure 
                    <apex:outputPanel id="treePanel">
                        <div id="jstree"> </div>  
                    </apex:outputPanel>
                    </div>

            </div>
        </div>
        </apex:form>
        </apex:page>