If you are working in Tree mode (see article Configuration of the item list tab), you can show assembly parts in both the Parts section and the Assemblies section of an item, or you can avoid listing redundant parts in the Parts section.
To use the following options, you must have enabled the Assemblies and Parts options in the Sections pane of the Display Settings>General tab.
In the Assembly Parts pane, select Show in Assembly list only to show item parts only under Assemblies.
The following screenshot shows items with parts listed under Assemblies only.
Select Show in Assembly & Parts list to list parts under Parts and under Assemblies.
The following screenshot shows items with parts listed under Parts and Assemblies.