Equivalent of StringBuilder for byte arrays

This is a simple one, and one that I thought would have been answered. I did try to find an answer on here, but didn't come up with anything - so apologies if there is something I have missed.

Anyway, is there an equivalent of StringBuilder but for byte arrays?

I'm not bothered about all the different overloads of Append() - but I'd like to see Append(byte) and Append(byte[]).

Is there anything around or is it roll-your-own time?