Bonsai is an East-Asian art form which utilizes cultivation techniques to produce, in containers, small trees that mimic the shape and scale of full size trees.
Light The main problem with keeping a tropical indoor Bonsai tree is that the intensity of light indoors is much lower than outside. Trees won’t die immediately when light intensity is too low, but growth will decrease, eventually weakening the plant. Therefore, make sure to place your Bonsai at a bright spot, preferably directly in front of a window facing the south.
Even when you have a window facing the south, chances are that the intensity of light is still too low. Artificial lighting can help, for example by using fluorescent lighting (with radiating growth-friendly spectra) or light-emitting diode lighting about 10 hours a day.
Humidity Another issue with keeping a tropical Bonsai tree indoors is that the tree needs a relatively high humidity, much higher than the indoor conditions of your house (especially when you use heating or air conditioning). You can increase humidity near your Bonsai tree by placing it on a humidity tray filled with water and by misting your tree a few times a day. What also helps is to circulate air from outside, by opening a window during the day.
Watering and fertilizing The most important rule is; never water on a routine. Ignore the label attached to your Bonsai tree which states you need to water every 'x' days. Instead, monitor your tree and only water when needed. It's best to know what variety of Bonsai you have to make the best judgement. Make sure to select the right tree species and take into account the specific care guidelines for indoor trees, and you will do just fine!