It is Manchester encoding on a 10MHz clock signal. Perhaps carrier isn't quite the right word.
I take back by correction. Thanks, and sorry. Manchester encoding really is a form of phase modulation (BPSK). It makes sense to think of it as a 10MHz baseband signal modulated by a 10MHz carrier, and therefore having a 20Mhz bandwidth.
The bandwidth is probably 20MHz, due to the Manchester encoding.