write linq query sitemapnode

我想写查询smn.ParentNode.ChildNodes。如果ShowInNavigation值为false，我不想显示。teleerik站点地图节点有这个att。怎么做?

using System;
using System.Web;
using Telerik.Sitefinity.Web;
using System.Linq;
using System.Data;
public partial class CustomTemplate_Navigation : System.Web.UI.UserControl
{
    protected void Page_Load(object sender, EventArgs e)
    {       
        SiteMapNode smn = SiteMapBase.GetCurrentProvider().CurrentNode;
        while (smn.ParentNode != null)
        {
            if (smn.ParentNode.ParentNode == SiteMap.RootNode)
            {               
                siteMapControl_verticaltree.DataSource = smn.ParentNode.ChildNodes;/*this line will be write query*/
                siteMapControl_verticaltree.DataBind();
                break;
            }
            smn = smn.ParentNode;
        }
    }
}

smn.ParentNode.ChildNodes.AsQueryable().Where(x => x.ShowInNavigation).ToList();

SiteMapNodeCollection coll = SiteMap.RootNode.ChildNodes;
IEnumerable<SiteMapNode> nodes = coll.Cast<SiteMapNode>();
var query = from node in nodes where Boolean.Parse(node["ShowInNavigation"]) == true select node;