if you were to use a smaller turbo to spool a big one.... how does it get plumbed up and how does the exhaust go

for instance....

exhaust leaves head and manifold flows to small turbo..... wastegate gets routed to downpipe.... downpipe feeds big turbo... to which another wastegate feeds its downpipe....


intake enters small turbo compresses and feeds big turbo...


or does air enter big turbo compresses air entering small turbo...


how does this kind of setup work...... diesels use a setup like this right???