There is a ledger, not a single chain.  The ledger is of n channels, which contain past transactions for that channel arranged as a tree.

IF you were to join and be presented with a 2 ledgers to sync from the genesis transaction, only one would be valid.  That would be the ledger where the first transactions are voted for by the bootstrap nodes.

So you can't have 2 ledgers to start with, unless all operators of the bootstrap nodes have signed the first transactions in both (which they wont)