private void btnRnd_Click(object sender, EventArgs e) { var val = rnd.Next(1, 999); var counter = 0; if (_tree != null) { _tree.Find(val); while (_tree.Find(val) && counter++ < 999) { val = rnd.Next(1, 999); } } inputTextBox.Text = val.ToString(); btnAdd_Click(btnAdd, new EventArgs()); }