Answer: It's not as easy as you might think. Since you have to work around the entire plant, you'll want one in a container, not one already planted in the ground. And, if you remove too much of the foliage all at the same time, the plant will brown out. Usually they green up in a year, so don't be too upset if this happens. Now for the process:
I have done this by fastening a rope to the top of the plant (I used a clothespin). Then spiraling the rope around the tree to the bottom, fastening it again. With sharp pruners carefully cut out everything that is holding the rope away from the trunk, leaving a nice wide spiral where the rope was. Once you have your shape, it is easy to keep it clipped. When you first do it, it may look sparse but as you keep it clipped, it will thicken up and look like the ones in the nurseries.
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