I have made a lot of Bargello quilts. It is very possible to skip the "sew into a tube" instructions. I find it much easier to cut if it isn't in that tube shape. I am making one right now that says to sew into a tube, but I am skipping that part.
So do what feels right for you. That I is a beautiful Christmas tree Bargello pattern. Hmmmm, I may just need that.
Dina