Ошибка CS0118: "TreeView" является "пространство имен", но используется как "тип" - C#

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.Utilities;
using System.Web;
using System.IO;
using System.Runtime.InteropServices;
using System.Xml.Serialization;
using Microsoft.SharePoint.WebControls;
using Microsoft.SharePoint.WebPartPages;
 
namespace TreeView.HelpDesk.VisualWebPart1
{
   [Guid("65f8b876-fbfd-4d50-942a-fe8ab317899c")]
    public class WebPart1 : System.Web.UI.WebControls.WebParts.WebPart
    {
        TreeView treeView;     //На эту часть кода ругается
        TreeNode rootNode;
       public WebPart1()
        {
              }
     protected override void RenderContents(System.Web.UI.HtmlTextWriter writer)
        {
            // render the control
            base.RenderContents(writer);
        }
 
        protected override void CreateChildControls()
         {
             
            base.CreateChildControls();
 
            // get the current site
            SPSite currentSite = SPContext.Current.Site;
            using (SPWeb currentWeb = currentSite.OpenWeb())
            {
                // set the tree view properties
                treeView = new System.Web.UI.WebControls.TreeView();
                treeView.ShowLines = true; // show lines
                treeView.ExpandDepth = 0; // expand non
 
                SPList list = currentWeb.Lists["Service_List_Test"];
 
                // build the tree
                rootNode = new System.Web.UI.WebControls.TreeNode(list.Title, "",
                           "", list.RootFolder.ServerRelativeUrl.ToString(), "");
 
                // loop down the tree
                GetFolder(list.RootFolder, rootNode, list);
 
                // add the root node to tree view
                treeView.Nodes.Add(rootNode);
            }
            this.Controls.Add(treeView);
            base.CreateChildControls();
        }
 
        public void GetFolder(SPFolder folder, TreeNode rootNode, SPList list)
        {
            // create a new node
            TreeNode newNode = new System.Web.UI.WebControls.TreeNode(folder.Name, "",
                               "~/_layouts/images/itdl.gif",
                               folder.ServerRelativeUrl.ToString(), "");
            try
            {
                // don't add the forms folder
                if (folder.Name != "Link")
                {
                    // loop through all child folders
                    foreach (SPFolder childFolder in folder.SubFolders)
                    {
                        // don't add the forms folder
                        if (childFolder.Name != "Link")
                        {
                            TreeNode trn =
                              new System.Web.UI.WebControls.TreeNode(childFolder.Name, "",
                              "", childFolder.ServerRelativeUrl.ToString(), "");
                            newNode = GetItems(childFolder, trn);
 
                            // add the new node to the tree
                            rootNode.ChildNodes.Add(newNode);
                        }
                    }
                }
            }
            catch { }
        }
 
        public TreeNode GetItems(SPFolder folder, TreeNode node)
        {
            //Get Items from childFolder
            SPQuery qry = new SPQuery();
            qry.Folder = folder;
            SPWeb web = null;
 
            web = folder.ParentWeb;
            SPListItemCollection ic = web.Lists[folder.ParentListId].GetItems(qry);
 
            foreach (SPListItem subitem in ic)
            {
                if (subitem.Folder != null) //Is Subfolder
                {
                    // create a new node for a subfolder and add items to it
                    TreeNode childNode =
                      new System.Web.UI.WebControls.TreeNode(subitem.Folder.Name);
                    node.ChildNodes.Add(GetItems(subitem.Folder, childNode));
                }
 
                if (subitem.Folder == null)
                {
                    TreeNode trn1 = new System.Web.UI.WebControls.TreeNode(
                                          subitem["Title0"].ToString());
                    node.ChildNodes.Add(trn1);
                }
            }
            return node;
        }
    }
}