WPF if else listbox

I have a project for my internship and i need to make something.

i have 2 listboxes 

listbox 1 goes to a folder1 and picks up files from there and shows it on the listbox.

listbox2 does exactly the same but from folder2.

now lets say i have a file named hello.txt in both of those folders.

both pick up the hello.txt and show it on the listboxes.

i want that ONLY listbox 2 picks up the file IF the file has the same name as the file in folder 1

i hope this is clear thanks.