I'm so late, this thread looks to be a classic too!
Okay, so technically I don't think this is a bun...but my ends are tucked in and my hair is pulled back...so it's my version. lol
I usually use a head band, twist the bottom of my hair up and then clamp all my hair together with whatever claw or hair stick I have at the moment. Sometimes I would tie my hair down before going out, to ensure no flyaways and "mold" the hair.
I did this style through relaxed, transitioning, the whole nine.
these used to be in my siggy - nothing new:
to get some views of the side/back (my hair was relaxed in these - and I loved having bangs then. thought it jazzed it up lol):
ETA: This worked for me, when I didn't think I had enough hair for pony tails or normal buns. I have thick/dense hair, but my hair was never "long" while I was relaxing.