display all xml files names in comboBox

I got code which writes all xml files that placed in xml folder (etc: xml/*.xml). The code is based on button click and textbox (if the user type "test" in textbox and click the button the code will generate xml file name "test.xml"). I would like to read the code and display all files names in comboBox4.

Reading the xml files:

private void comboBox4_SelectedIndexChanged(object sender, EventArgs e)
{
   new FileStream("xml/*.xml", FileMode.Open);
}

As you can see there is FileMode.Open, and I set the directory to read all files in folder xml. Now I have no idea how to print all files on comboBox4 (my combo box name is comboBox4).

Any ideas how can I print/display each xml file name on comboBox4?