Another consideration for you.
You can create a nested list within the tree and the panes using the listbuild() function. With this, and the help of custom fields, you can create what you want.
For example, I have a series of volumes of Cafe del Mar albums.
I created two new custom fields, called [my album] and [myseries], where [my album] contains the root of the album name (in this example, I used "Cafe DEL MAR"), and where [myseries] contains the volume specifier (eg. "Vol. 2", "Vol. 3", "Dreams Vol. 4").
Using listbuild(), we can create a nested list structure such as:
Audio
==>Artist/Album
====>(Multiple Artists)
======>Cafe DEL MAR
========>2006
========>Dreams
========>Dreams, Vol.2
etc.
In the expression below, I use the standard [album] if [my album] is empty, and [year] if [myseries] is empty. Note: I have only tagged the Cafe del Mar series so you see all the other [album]'s in the list, and I did not set the [myseries] value for Cafe del Mar, Vol. 13 so it shows under Cafe DEL MAR/2006.
listbuild(1,\,[album artist (auto)],if(isempty([my album]),[album],[my album]),if(isempty([myseries]),[year],[myseries]))&datatype=