How to postback the checkbox value in treeview when each time it is checked? (in asp.net)

for example
we have the <treeview control coding here>
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<asp:TreeView ID="TreeView1" ImageSet="Msdn" ExpandDepth="1" CssClass="text1"
ShowCheckBoxes="All" runat="server" Width="600px">
<RootNodeStyle Width="400px" ChildNodesPadding="1px" Height="20px" CssClass="text1"
BackColor="White" />
..............
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and the value for that are assigned to it from the database when the page is loaded

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TreeNode root = new TreeNode();
root.Text = ParentNode[loop, 1];
SqlConnection SqlCon = new SqlConnection("")

SqlCon.Open();
SqlCommand SqlCmd = new SqlCommand( sql statement , SqlCon);
while (Sdr.Read())
{

ParentNode[count, 0] = Sdr.GetValue(Sdr.GetOrdinal("SysMenuID")).ToString ();
ParentNode[count++, 1] = Sdr.GetValue(Sdr.GetOrdinal("Name")).ToString();

.............
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now the problem is when the page is loaded .. we get all the values for the checkboxes displayed using the Treeview control

but when we click the check box and submit the page ..how to get the value of the check box ..?

when try to get the id of checked box

foreach(TreeNode root in TreeView1.CheckedNodes)
{
checkmessage.Text = how to get the ParentNode id ..?

}