Treeview is not collapsing.

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C#

ASP.NET

XML

SQL-Server

hi, this works good. but, tree is not collapsing in output. it expand all node.

namespace xmltreeview
{
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
TreeView1.CollapseAll();
XmlDataSource1.Data = GetHierarchicalDataFromSqlServer();

}
string GetHierarchicalDataFromSqlServer()
{

string xml = string.Empty;


string queryString = @" sqlquery";
string connectionstring = ConfigurationManager.ConnectionStrings["sqlconnectstring"].ToString();
using(SqlConnection connection=new SqlConnection(connectionstring))
{

SqlCommand Selectcommand = new SqlCommand(queryString, connection);
connection.Open();
XmlReader xr = Selectcommand.ExecuteXmlReader();
xr.MoveToContent();
xml = xr.ReadOuterXml();
TreeView1.CollapseAll();
}

return xml;




}

}

}


pls help me