overflow scroll

<div  style="float:left;width:23%;height:550px; overflow:scroll;" >
<div style="float:left;width:100%;height:auto;" class="treeMenuHeading">Banks Name</div>
<%int i =0; %>
<s:iterator value="bankNameParentTree1stList">
<%i++;%>
<ul id="treeview" class='treeview' style="font-family:Arial;font-size:12px;font-weight:bold;text-align:left;">
    <li class="inner">
        <span class='plus' id="<s:property value='bank_id'/>" onClick="callBranchName2ndTree(this.id,<%=i%>)">
             <s:property value="bank_name"/>
        </span>
    <ul id="showBranchName2ndTreeDiv<%=i%>"></ul>
    </li>
</ul>
</s:iterator>
</div>