Custom Views filter for multi-level taxonomy
in Relationships you add:
 Taxonomy: Parent item

then in Filters add:
 Taxonomy: Term ID, set Relationship to the above Parent, and the Operator: Is empty(NULL)

This way you only get the top level terms, because they don't have parents. Or you set it to Not empty(NOT NULL) to get the child terms.

I hope this method helps you in some way.