Yes I think so. The question is asking for the biomass not the numbers. True, there is only one oak tree, but its mass supports that whole system. The oak tree is the producer in this system. The caterpillars eat the tree leaves, so they are the Primary Consumer. The toads eat the caterpillars so the toads are the Secondary Consumer. The snake eats the toads and is the tertiary consumer. So yes, it would be shaped like a regular pyramid.
