用Linq加载treeview

用Linq加载treeview时代码如下：

        private void BindRootTree()
        {
            this.tv_emp.Nodes.Clear();

            this.BindTreeView(null, null);
        }

        private void BindTreeView(TreeNode tn,DEPARTMENT1 dept)
        {
            DataEntityQuery<DEPARTMENT1> query = DataEntityQuery<DEPARTMENT1>.Create();
            int parentID = dept != null ? dept.id : 0;  //判断父节点
            var v = from c in query
                    where c.partentid == parentID
                    orderby c.id
                    select c;
            IList<DEPARTMENT1> xlist = v.ToList();
            foreach (var item in xlist)
            {
                TreeNode node = new TreeNode();
                node.Tag = item;
                node.Text = item.name;
                if (tn != null)
                {
                    //添加子节点
                    tn.Nodes.Add(node);
                }
                else
                {

　　　　　　　//添加父节点
                    this.tv_emp.Nodes.Add(node);
                }
                this.BindTreeView(node,item);
            }
        }