private void assertCommonB(Traversal<Vertex, Tree> traversal) {
        final Tree tree = traversal.next();
        assertFalse(traversal.hasNext());
        assertEquals(1, tree.size());
        assertTrue(tree.containsKey(convertToVertexId("marko")));
        assertEquals(1, ((Map) tree.get(convertToVertexId("marko"))).size());
        assertTrue(((Map) tree.get(convertToVertexId("marko"))).containsKey(convertToVertexId("josh")));
        assertTrue(((Map) ((Map) tree.get(convertToVertexId("marko"))).get(convertToVertexId("josh"))).containsKey(convertToVertexId("lop")));
        assertTrue(((Map) ((Map) tree.get(convertToVertexId("marko"))).get(convertToVertexId("josh"))).containsKey(convertToVertexId("ripple")));
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/TreeTest.java