The most of the root nodes in the Music Library can be customized to fit your specific needs.
By default all root nodes in the Music Library comes with a predefined order and child nodes, which you can change.
The following root nodes are customizable:
Artist
Album
Title
Genre
Rating
Release Year
Recording Year
Mood
Situation
Release Type
Library/Volume
User Defined
Quality
Series
Grouping
Publisher
To customize a root node in the Music Library, select the node, right-click and select "Customize.." from the context menu.
The following dialog will be shown:

Select the fields you would like to use from the right list and click the "< Add" button to add them to the Active List (shown to the left).
You can change the order of the selected fields by selecting a specific field from the list and move it up/down by clicking the "Move Up" or "Move Down" button.