A Dwarf Black Olive makes an excellent indoor bonsai. They have lots of sharp thorns, so handle with care.
Unlike most species of trees, when left to grow on their own, they will grow into near perfect "bonsai shapes" with little or no trimming or wiring.
They do well indoors but should be kept outdoors in warm weather. They like direct sun, but avoid direct mid-day sun in the middle of summer.
While they can survive temperatures in the 40's, they do best when kept in the 60's and above year-round.
Root work is best done in mid-summer, and drastic root-ball reduction should be avoided. It is better to reduce the root-ball over a few years.
Keep them well-watered for best results. They do not like dry soil!