is there any way through which we can upsert list of list of accounts?

I want to update list of list of account. I am getting list of accounts from many sources, now i want to update them.

list<list<sObject>> la=new list<list<sObject>>();
la.add(accountList1);
la.add(accountList2);
upsert la;
Its throwing an error, is there any way through which we can upsert list of list of accounts?