fund attributes - product category

Dear experts,

We are setting up Funds with attribute PROD_CAT (Product Category).

I am not able to add root product hierarchy R3PRODHIER in the Fund attribute field (it is throwing an error - Invalid Product Category ID R3PRODHIER).

But it allows me to add the product categories below R3PRODHIER in the Fund attribute field.

I wanted to know if it is possible to add R3PRODHIER in the Fund attribute field.

Do I have to do any configuration settings for that.

I can see only the following product-related attributes PRODUCT, PROD_CAT & PROD_GRP available in spro.

So is there any other way where I can add the root product hierarchy.