placing an empty bundle on a bundle on a bundle on a bundle on a bundle on a bundle on a bundle on a... you get the point. when trying to empty said bundle, the game hangs. you can still move and break blocks, and particles and sounds still play, but you can't hit mobs, place water, or anything that requires a block update. items don't appear either, when chopping wood, etc.
when trying to log out, the game hangs. wow, the server-kill possibilities...
There's a limit on this, see MC-203567.
The only way to nest a bundle so that it crashes a server is by using commands, at which point you already have plenty of possibilities to crash a server.