presto-main/src/main/java/io/prestosql/sql/planner/planprinter/TextRenderer.java/Indent/forChild
class Indent:        public Indent forChild(boolean last, boolean hasChildren)
        {
            String first;
            String next;

            if (last) {
                first = pad(LAST_NODE, 3);
                next = pad("", 3);
            }
            else {
                first = pad(INTERMEDIATE_NODE, 3);
                next = pad(VERTICAL_LINE, 3);
            }

            return new Indent(nextLinesPrefix + first, nextLinesPrefix + next, hasChildren);
        }