You need to identify the central "leader" or branch that is growing most vertically, and train it to continue to grow vertically until it reaches the height that you want the trunk to be, and the prune it off to force branching at that height. You will need to remove all the other side growth, and continue to pinch off any new attempts at side growth. If you don't have a nice vertical branch to train to be the trunk, you might need to cut the tree off closer to the ground, and let it send up some new branches, and pick and train one of those to be the trunk of your "new" tree (while also removing all other new growth).

I would like to carry georgia peach's question a step or two : 1. Which form is more productive, bush or tree? and 2. Could bush form be carried linear, like a hedge from a single plant? I ask question 2 because two of my fig trees have sprouts coming up two feet or more from the main branch, and I assume that in time this could be extended in any given direction. Has anyone ever tried, or seen, this form?.....Elder

I have a Celeste fig. It has a nice straight "trunk" about 43 inches tall. Then it "branches" out from that point to form a nice ball..kind of like an "afro"..
Is this ok? The tree is happy it seems. I haven't added any support. Doesn't seem to need it.
The tree is 3 years old.
What can I expect from here. Also, when it does get real big, can I keep it in bounds a bit? Thank you!

I don't know about productivity, but picking and dealing with birds, etc. is definitely easier on a shorter bush-shaped plant. I have one "tree" which is almost 10 years old, and still only about 3-1/2' tall. Next year it will be about 3-4" taller when I am done pruning. All my newer plants will be similarly trained. I am sure you can "espalier" a fig tree, to be sort of long and narrow. It is just a matter of pruing and persistence, I would think.

I'll have to find the source, but I remember reading the ideal fruiting zone of a tree is 5-6 feet in height. Meaning if you want an eight foot trunk on your tree, the fruit zone will be from 8-13/14 feet. One of my in ground trees is about 14 feet tall now. It is not so easy to harvest the fruit from the top, however this is mostly due to it being in bush form and having to work around the lower branches. I use a small step stool and pull the branches down to harvest. One can prune to shorten the fruit zone to a couple of feet resulting in decreased production.

Elder, someone post pics of fig trees which grew from suckers and formed a hedge along the side of a highway in Sacramento(I think) in this forum. Perhaps someone remembers the link to the pics.

~james