Look across multiple disks for duplicate files and directory subtrees
WPF Treeviewcode influenced by
https://www.codeproject.com/Articles/26288/Simplifying-the-WPF-TreeView-by-Using-the-ViewMode
https://www.codeproject.com/Articles/1204663/Advanced-WPF-TreeViews
https://stackoverflow.com/questions/5487927/expand-wpf-treeview-to-support-sorting