How to select random object from selected checkboxes

So what I am trying to do is following: I have 5 main checkboxes and each checkbox has 3 child checkboxes. After selecting some of the boxes, I am trying to select a random item of the selected boxes and then show it in a text box.

My first question is that is TreeView the way to go? It seems to be the best way to achieve hierarchical view.

And second question is to pick the random item do I need to insert the items to a list/array first?