What you want are the little dark green trees in the christmas department. You see them a lot with the christmas villages. They're called bottle brush trees because they're made like old-fashioned bottle brushes.
My local Walmart has them in packs of 7 or 8, dark green. They had packs of white ones and individual trees earlier in the season, but sold out. (Your Walmart may restock more often than mine; a few years ago they ran out of christmas wrap in mid-December and didn't restock. I still don't trust them, and buy everything as soon as I see it). The sparkley trees may not bleach well, either.
I suppose you could start with actual bottle brushes, but I don't think they make them from sisal any more, probably plastic that wouldn't bleach or dye the same.
The larger trees that look like they're made of fat pipe cleaners/ chenille stems ARE plastic and don't bleach well. Ask me how I know.
those are lovely!
stupid question...where does one get bottle brushes?