presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/GraphvizPrinter/visitFilter
class GraphvizPrinter:        @Override
        public Void visitFilter(FilterNode node, Void context)
        {
            String expression = node.getPredicate().toString();
            printNode(node, "Filter", expression, NODE_COLORS.get(NodeType.FILTER));
            return node.getSource().accept(this, context);
        }