I read from some document, sounds like the first several bytes shows
the version, which starts from 0.

So for X509.v1, I should see the first byte "0", for v3, I should see
the first byte "2".

But when I decode the x509.v1 and v3's certificate, it appears the
format is not that way,

the first two bytes: 48, -126,

then for v1, the third byte is 2, and for v3, the third byte is 4.

Any idea on that?

Thanks