Got the answer:
private void AddNew_Click(object sender, EventArgs e)
{
Stream myStream;
SaveFileDialog saveFileDialog1 = new SaveFileDialog();
saveFileDialog1.InitialDirectory = @"C:\";
saveFileDialog1.DefaultExt = "txt";
saveFileDialog1.Filter = "(*.txt)|*.txt";
saveFileDialog1.FilterIndex = 2;
saveFileDialog1.RestoreDirectory = true;
if (saveFileDialog1.ShowDialog() == DialogResult.OK)
{
if ((myStream = saveFileDialog1.OpenFile()) != null)
{
string FileName = saveFileDialog1.FileName;
TreeNode newNode = new TreeNode(FileName);
newNode.SelectedImageIndex = 1;
tvwACH.SelectedNode.Nodes.Add(newNode);
newNode.Nodes.Add("FileHeader");
newNode.Nodes.Add("BatchHeader");
newNode.Nodes.Add("EntryDetail");
}
}
}