private void button_FT_BDD_Click(object sender, EventArgs e)
        {
            if (_rootFaultTree == null)
            {
                MessageBox.Show("please choose input file and click ok!");
                return;
            }
            VisualBinaryTree BDDT = new VisualBinaryTree(_rootBDDTree);

            BDDT.Show();
        }
        private void button_UFT_meta_BDD_Click(object sender, EventArgs e)
        {
            if (_rootFaultTree == null)
            {
                MessageBox.Show("please choose input file and click ok!");
                return;
            }
            VisualBinaryTree MetaUT = new VisualBinaryTree(_rootMetaTree_Uncertainty);

            MetaUT.Show();
        }