Ethereum is not an alt to Bitcoin. Ethereum is Web 3.0, the backend of a peer-to-peer, decentralised Web, that may one day replace the current Web 1.0.
The tokens are ETH (Ether), which could also be used as an alternative payment system like BTC, however they aren’t really. (If the Ether tokens are used the same way as BTC tokens, then they could be regarded as an altcoin.