Trees are beautiful, and help to provide a natural way of air filtration for people during the day. True, there are indoor plants such as the peace lilly, spider plant, garden mums as well as various ferns that do a most excellent job of filtering out toxins from our or office environment or home environment air. These plants are not everywhere, and when they are available for sale, they cost a fair amount of soft currency, or cash, per room. Between this and air filters, you can render your air breathable. Still, trees are less likely to be stepped on than smaller plants would be in the great or still working on being great again, outdoors.