Also, I see there is a Method in there "GetFilesInDir" which accepts a MASK string to specify the types I want accumulated but not for the viewing of the TreeView ? It shows all the files and I only what the files of interest to show in the branches..
I tried to introduce a Mask property to be used by GetFilesInDir. The consequence, however, is that the Mask is applied also to directory names, and this is probably not what you want. Certainly, this can be fixed but requires some larger changes with more intense testing than I can do at the moment...
Then I tried to introduce an event OnAddingFile with a boolean var-parameter "Accept" to prevent a file from inclusion in the file list under some circumstances. But this failed too because GetFilesInDir is a class procedure which does not have access to the event... Again, this can be made, but would break the code in existing projects using GetFilesInDir without creating a class instance.
So, in total, no easy way...
Why don't you combine a folders-only ShellTreeView with ShellListView? That's way I always have been using TShellTreeView. And, in fact, it is very useful this way.