Need Scroll Bar for Drop Down List populated by ng-options

I have this code which populates the drop dopwn menu:

echo "<div class='form-group'>";
echo "<label for='show'>Show:</label>";
echo "<select class='form-control' id='filterText' ng-model='filterText' ng-options='show_name for show_name in filterList'>"; // Show Type Dropdown
echo "</select>";
echo "</div>";

I want to be able to only show maybe 8 options then be able to scroll down to see the rest. How do I go about doing this? When I adjust the height, it just adjusts the height of the actual field instead of the drop down size.

This is not what I want:

TURNS OUT IF THE LIST IS LONG ENOUGH, IT WILL AUTOMATICALLY ADD A SCROLL BAR. THIS IS NOT ORIGINALLY WHAT I WANTED. IT WOULD BE EASIER IF THERE WERE 8 SHOWS SHOWN TO START WITH AND BE ABLE TO SCROLL THROUGH THE REST.