private void createGraphFromDef_Click(object sender, EventArgs e)
 {
     try
     {
         if (treeDef.Text != "")
         {
             CreateGraph(TreeBankEngine.ExtractNode(treeDef.Text, true));
         }
     }
     catch (Exception ex)
     {
         MessageBox.Show("Error:  " + ex);
     }
 }