Displaying Sibling links if no Children present

Hi,

I am trying to edit the Navigation template to show the sibling links when no child nodes are present.i have  tried the below code but getting error- Cannot
convert type 'System.Web.SiteMapNodeCollection' to
'Telerik.Sitefinity.Web.UI.NavigationControls.SitefinitySiteMapDataSource'

 Please help me know the alternative solution to bind child nodes in navigation container, if child nodes are not present then  should bind the siblings

<navigation:NavigationContainer runat="server" DataSourceID="dataSource">
    <Templates>
        <navigation:NavigationTemplate runat="server">

            <Template>
                <li>
                  <navigation:NavigationContainer ID="NavigationContainer1" runat="server" DataSource='<%# ((SiteMapNode) Container.DataItem).ChildNodes %>'>
                        <Templates>
                            <navigation:NavigationTemplate ID="NavigationTemplate1" runat="server">

                                <Template>
                                    <li>
                                        <a id="A1" runat="server" href='<%# NavigationUtilities.ResolveUrl(Container.DataItem) %>' target='<%# NavigationUtilities.GetLinkTarget(Container.DataItem) %>'><%# Eval("PageTitle") %></a>
                                    </li>
                                </Template>
                                <SelectedTemplate>
                                    <li class="active">
                                        <a id="A2" runat="server" href='<%# NavigationUtilities.ResolveUrl(Container.DataItem) %>' class="active" target='<%# NavigationUtilities.GetLinkTarget(Container.DataItem) %>'><%# Eval("PageTitle") %></a>
                                    </li>
                                </SelectedTemplate>
                            </navigation:NavigationTemplate>
                        </Templates>

                    </navigation:NavigationContainer>
                </li>
            </Template>
            <SelectedTemplate>

            </SelectedTemplate>
        </navigation:NavigationTemplate>
    </Templates>

</navigation:NavigationContainer>

Thanks,

Arun