Vertical scrollbar not visible and items are passing over the usercontrol

[akinbender]

Hi,

First of all, this repo helped me a lot, so thank you!

Consider the treelistview photo in the readme.md. In my case, if I add more "est"s in "multiple options" item until the list reaches to the border of the usercontrol, the vertical scrollbar does not appear.

But if I add enough "multiple options" items to the list until the list reaches to the border of the usercontrol, the vertical scrollbar appears. I tried to solve this issue, however i had no luck so far..

Best Regards