I dont think this is what is meant by hierachy. With hierachy its shown to to have several products, each product having its "sub products" (for example to set up a conference you need a venue, attendees, speakers etc.), and each sub products have their own sub items. So in that way its hierarchical. But being hierarchical doesnt mean there a certain order of products that need to be done first. This can be shown in a flow chart, based on the product breakdown (which products are interdependent, which need to be created first etc.).