Photographer Natalie Fertig wraps up the Christmas tree-selling season by talking to New York’s sidewalk vendors, many of whom hail from north of the border, work shifts that last much of the day, and sometimes sleep in a van. There are benefits too: the travel, after-hours camaraderie, drinks, and if you’re on the Upper West Side, a smörgåsbord of dinner options from the people who live in the buildings around you.