Indoors,they become very susceptible to root rot. Much light,warm,and air circulation is needed. Hard to over winter by a window.

Lighting is poor inside the house from the picture you took. The window only provide light for a small portion of the day.

You have to slowly get the plant use to the shade. Slowly shade the tree outdoors for a few days before bring it indoors. If it can't survive the partial shade outdoor, it probably won't survive indoor.

The tree needs light just as much as it needs heat. You can put it in a heated room without light and it will die.

The outside sunlight is brighter than you think. You can buy a light meter for about $30 and see the difference in intensity.

Use "daylight" light bulbs instead of the "soft white" light bulbs. They use the same wattage but give off a brighter intensity light.

The closer the plant is to the bulb, the higher the intensity of the light. If you have a ceiling light, the plant will have more light intensity on the table instead of sitting on the floor.

Photosynthesis uses mainly blue and red rays from the light spectrum to produce energy. Indoor marijuana growers use the blue lamp. If you don't mind spending extra money, you can get the blue lamps.