It doesn't take too much effort to realise that there is no such thing as an indoor plant, tree, bonsai. All, so called, indoor bonsai are difficult to keep alive indoors, to get the best results you need to be able to keep them outside during the winter months and bring them indoors during winter and cold spells. Whilst growing indoors, most trees need good light levels, without standing in the window sill; and they need spraying with room temperature water, several times per day. Ficus spp need annual root pruning and the use of bottom heat after this pruning to promote fresh, vigorous regeneration of root. You will hear stories of trees living indoors that are neglected yet still survive, but the idea of growing a bonsai is to always maintain a healthy, vigorous tree.