I've been in a few places with inside trees: Most notably, "Arby's" (a fast-food restaurant) and nursing homes.
Sometimes, places simply have a hole in the foundation that allows access to the ground. These holes often have more dirt on top and can support a rather tall tree. Other places have large containers of dirt which support smaller trees.
It really isn't much different than folks planting trees in the middle of the sidewalk or trees/shrubs in large pots outside, honestly, except for the fact that it won't rain indoors.
Sometimes, places simply have a hole in the foundation that allows access to the ground. These holes often have more dirt on top and can support a rather tall tree. Other places have large containers of dirt which support smaller trees.
It really isn't much different than folks planting trees in the middle of the sidewalk or trees/shrubs in large pots outside, honestly, except for the fact that it won't rain indoors.