UpdatePanel does not update

I have the following updatePanel:

<asp:ScriptManager ID="ScriptManager1" runat="server" ChildrenAsTriggers="true" >
        <Scripts>

        </Scripts>
    </asp:ScriptManager>

    <asp:UpdatePanel ID="panelTreeView" runat="server"   UpdateMode="Conditional"> 
          <ContentTemplate>
<div class="easy-tree">

     <asp:TreeView  ID="TreeView1" runat="server" ImageSet="Arrows" ForeColor="Black"     OnSelectedNodeChanged="TreeView1_SelectedNodeChanged" >
         <HoverNodeStyle Font-Underline="True" ForeColor="#5555DD" />
         <NodeStyle Font-Names="Tahoma" Font-Size="10pt" ForeColor="Black"     HorizontalPadding="5px" NodeSpacing="0px" VerticalPadding="0px" />
         <ParentNodeStyle Font-Bold="False" />
     <SelectedNodeStyle Font-Underline="True" ForeColor="#5555DD" BackColor="#E2D2D2"                         HorizontalPadding="0px" VerticalPadding="0px" />

</asp:TreeView>

    </div>
              </ContentTemplate>
    </asp:UpdatePanel>

I want to update the treeview at a given time.

codebhind method:

public metodoQualquer(){
this.panelTreeView.Update();
}

But nothing happens.