BND vs Treasury vs CD

Wife and I are 46. I switched to self directed at Fidelity in March. I made a very rash decision to leave our financial advisor in good way. I just did it and told wife I had everything figured out. That was mostly true. I had no understanding of bonds.

I got all the equites set up and felt comfortable with all that. Investing almost everything in FZROX was not that hard to do.

When it came to bonds I stumbled upon BND as a fund to invest in bonds. Just needed to get the portfolio finished so I could show wife portfolio is set up as the allocation we agreed to. Now I want to actually learn about bonds/cd//BND.

I understand what they do in broad strokes but do not understand why I would invest in bond over a CD when the yields are nearly the same for the time frame. We are not thinking of retirement till 60-65. I can get a 10 year treasury or cd. That gets us to 56 and then create a ladder to get us into retirement.

Why would I choose a treasury over a CD, or vice versa?
Why would I choose BND over either of these?
If I wanted to get more aggressive why not change my allocation to invest in a dividend fund instead of bond/cd?

I am more hung up on this part of the portfolio than the equity side. Any help suggestions or comments are greatly appreciated.