Can I Upsert List of List of Opportunity?

Using the upsert operation, you can either insert or update an existing record in one call. To determine whether a record already exists, the upsert statement or Database method uses the record’s ID as the key to match records, a custom external ID field, or a standard field with the id Lookup attribute set to true.
1. If the key is not matched, then a new object record is created.
2.If the key is matched once, then the existing object record is updated.
3. If the key is matched multiple times, then an error is generated and the object record is neither inserted or updated.