I am making a 'spooky' tree out of modeling chocolate and am trying to figure out the best way to attach the branches to the tree trunk. I am going to put a small wire into each branch, but I also need a bonding agent to 'glue' it. Any suggestions?

Hi I can't exactly answer your question but I saw somewhere recently the stalks used off a bunch of grapes dipped in chocolate used as trees . They looked great . Good luck

If you are already making the tree out of chocolate, can you just use melted chocolate to weld the limb to the trunk and hold them or prop them together long enough for the chocolate to harden enough to keep them together?

This is the most recent thread about the grape stem trees (and other types) that I know of:
http://cakecentral.com/cake-decorating-ftopict-732130-grapes.html

I don't know if I'm too late, but I just made a "spooky" tree out of modeling chocolate - I have pictures posted on my profile with my angry birds figures. If this is something like what you want, here's how I did the tree:

I made all the branches first and let them sit and harden a little.
Then I made the trunk and molded some lumps where I wanted the branches to go. Then I put a large hole in each lump using a ball tool.
I inserted the branches into the holes, then used the lumps for securing the branches - I molded them around the base of the branches and blended.

I did not use any wires or toothpicks or anything like that - the tree was 100% modeling chocolate.
I don't know if this would work with a larger tree with longer branches, but it worked perfect for me. The tree was pretty solid