richtextbox text appending- Urgent

I have made Function For Appending Text To Current Cursor Position in RichText Box
Try it

        private void btnSendToRtf_Click(object sender, EventArgs e)
        {
            appendtext_to_cursor_position(richTextBox1, listBox1.SelectedItem.ToString(), richTextBox1.SelectionStart);
          
        }

        void appendtext_to_cursor_position(RichTextBox rtf, String str, int positiontoinsert)
        {
            int CurrentCeret = rtf.SelectionStart + str.Length;
            rtf.Select(positiontoinsert, rtf.TextLength - positiontoinsert);
            str+= rtf.SelectedText;
            rtf.SelectedText = String.Empty;
            rtf.AppendText(str);
            rtf.SelectionStart = CurrentCeret;

        }

Happy Coding :-)