Tree Prompt

[Jeka]

Hi,
Maybe someone can answer my question.

Using Cube.

Created an Optional Tree prompt with (rootMembers([Ledger].[Department].[Department]) )
then
I created a member in the report with ([Ledger].[Department].[Department])

When user selects for example 2nd level on in the Tree prompt then he can drill down in the report.

Issue: If the user doesn’t select anything in the tree prompt then after running the report i see every single level(and all the members of all levels) of the Department Hierarchy in the report.
How can i make it if the department not selected then only show the highest level NOT All levels ?

Thank-you