When I was a kid my mom worked at a shop where they built architectural models. She took me to work with her a few times and I got to see how they made the trees they would use for landscaping around the buildings. They would strip copper wire out of old electrical cords and twist bundles of it together to make trunks and branches. I didn't have any cords I was willing to sacrifice, but I got some beading wire and used a similar technique to make this model of the Whomping Willow from Harry Potter.
Here's how I made this, in case anyone wants to try it:
I used 26g wire, but I wish I'd gone for 28 or even 30g. The 26g was kind of hard to work with.
I cut the wire into lengths of about 4 inches. I think I used 24 pieces of wire - you need enough to make a good number of branches so your tree looks full instead of spindly. I didn't use enough on my first attempt
Once you've got your wire pieces, twist them together starting at the bottom. If I'd used thinner wire I may have been able to do this by hand, but I had to use two pairs of pliers. (Sorry my pliers look so grody, I put tape on them so they won't scratch my aluminum chainmail rings.) When you have as much trunk as you want, peel off a small bundle of wires for your first branch. Start twisting the new bundle independently of the trunk, splitting off and twisting smaller groups to make twigs until you run out of wire. Then go back to the trunk, twist a little more, and peel off another branch.
Keep peeling off and twisting branches and twigs until you run out of tree. Now you have to decide what kind of tree you want - for a standard, generically tree-looking tree you would trim your wire ends into a vaguely spherical shape, then bend the end of each twig slightly upward. Since I was making a willow, I curved all my wire ends down and then trimmed them to what I felt were appropriate lengths.
After that, since this is a tree that hits people, I curled the ends of its branches into "fists."
Ford Anglias, beware!