No tree is a bonsai tree naturally. Bonsai just refers to the way a tree is trained.

Your tree is not a true pine. It's Podocarpus macrophyllus. This species can be trained as a bonsai or left alone. There are many stems because it's probably been grown from a clump of cuttings. If you want it to be bonsai you'd need to research how to train it. There are many styles and some are a clump rather than a single stem.

This species is not a suitable subject for a house plant. It needs to be outside. If you have cold winters it can be kept in a very light cool place, like a greenhouse or glazed porch, until spring.