Trigger on indexed view
The base table insert plan incorporates operations necessary to keep the indexed view synchronized with the base table as defined by the view definition. This part of the plan is automatically generated and cannot be disabled, or made to call the instead of trigger logic on the view instead. The contract of an indexed view is that it will always materialize the query stored in the view.

The main purpose of instead of triggers on views (indexed or otherwise) is to make them updatable when they wouldn't be otherwise. The question doesn't explain what you need to achieve, but it seems an indexed view is not the right mechanism. You might need a separate table instead of a view. Please ask a follow-up question if you want help solving the underlying problem, and ideally provide a self-contained reproduction script.