In her book, "The Tree Collectors," writer and illustrator Amy Stewart recounts stories of people who harbor tree obsessions, from the designers of leafy urban spaces, to those who lovingly cultivate ancient tree species. Correspondent Martha Teichner talks with Stewart, who calls planting a tree "an act of hope"; Kao Saelee, who grows tropical fruit trees at his California home; and plant scientist Reagan Wytsalucy, whose goal is to revive the peach trees of her Navajo ancestors.