You can configure second level navigation views in Siebel Tools for your Siebel application as required.
To configure second level navigation views for your application
In Siebel Tools go to the Object Explorer and select Screen.
Query for the screen that you want.
In the screen view, add the new view.
For each view that you add:
Set Type to Aggregate View.
Set the sequence number for the view.
Do not set the Parent Category for the view.
Update the repository and deliver the updates, then start the Siebel application.
The new view appears alongside the other second level aggregate views in the UI.