It has been suggested before
In tree mode, multiselection is not supported, nor will I make it so. The biggest problem is the native windows treeview does not support multiselection so I would have to code a custom treeview control completely by myself. Too much work and not worth my time.
The list mode does support multiselection though, this was my 'reply' to the request. My tip would be, in tree mode, find the first and last index that you want to keep in the file, then switch to list mode, and select all the nodes at once using ctrl/shift etc., and then delete... I've done this many times myself, and you can do it in a couple of secs.
I'm sure you can do this faster in hex, but I want to see you insert a 3D model with tmaps from 4 obj-files in hex. I'll wait for a few days, let me know!
[edit] As far as tutorials are concerned, sometimes it's better to just keep the explanation simple, which sometimes involves more handwork. If every trick or shortcut has to be written down, tutorials become too lengthy and/or with too many side paths and are more difficult to understand... It's always hard to determine what is the best way to explain things. This is also true for S3D, there is no 'set' way to achieve things. One can do certain things in more than one way in most cases...