Patio trees, also commonly called "standards," are a wonderful garden design element. They are especially useful to add height or a vertical element to a small garden space.
Another use they serve is to provide a visual screen while still leaving space below to plant other shrubs or flowers.
There is a wonderful selection of plants available in standard form these days. Here are some suggestions for their use:
Privet, Eugenia, or Hawthorne
Chinese Fringe Flower (Loropetalum)
Olive (Olea europaea)
Along with standards, there are also many types of dwarf trees that serve the same purpose.
One of my very favorites is the Young's Weeping Birch, especially the fascinating serpentine style. I think its the perfect accent for an Asian garden.
Or, the weeping Blue Atlas Cedar
So, the next time you are looking for a unique plant to fill a narrow space, consider a standard. Even if your garden center doesn't have one on the grounds, you can make a special request for whichever type of standard you are seeking.