saving data in datatable using recursive function

Question

In the below function I have a DataTable which resets during recursion of the function. How can I solve this problem?

I have to create table once and add rows repeatedly in each repeat of the function.

 

Please help! 

 

 

private DataTable GetSelectedTreeNodes(TreeNode parentTreeNode)

{

   DataTable tvp = new DataTable();

   tvp.Columns.Add(new DataColumn("Suburb"));

   if (parentTreeNode.Checked)

   {

      ListBox1.Items.Add(parentTreeNode.Text);

      tvp.Rows.Add(parentTreeNode.Text);

      tvp.Rows.Add(parentTreeNode.Text);

   }

   if (parentTreeNode.ChildNodes.Count > 0)

   {

   foreach (TreeNode childTreeNode in parentTreeNode.ChildNodes)

   {

      GetSelectedTreeNodes(childTreeNode);

   }

}

return tvp;

}