These tutorials provide step-by-step guidance on organizing feature trees and creating custom library features: How to Add Features into a Folder in SOLIDWORKS YouTube · JOA Designs
You can drag and drop additional features into the folder or use Expand All / Collapse All to manage the tree's visibility.
Right-click the new folder and select Rename tree item (or use F2 ) to give it a descriptive name like "Mounting Features" or "Nowy Features".