Dependent dropdown in a form

Hello,
I need to create a form for end users to assign  a cross-dimension (direction and activity) to 2 new dimensions (Analytical Dim level 1 and Analytical Dim level 2). To do this, I was thinking of:

1. Creating a table with the direction/activity cross and the associated data.
2. Creating 2 metrics with the direction and activity dimensions A. to select: Analytical Dim level 1 B. to select: Analytical Dim level 2

However, I would like the selection of "Analytical Dim level 1" to only display the child items of Analytical Dim level 2. Is it possible to do this and if so, how?

Thank you in advance for your help.