While not generally referred to as 1-tier trees, the simplest tree-type topology is that of a single switch. For example, the CN5000 Switch allows for 48 400 Gbps native SuperNIC links (links between a switch and a SuperNIC), or 80 200 Gbps subdivided SuperNIC links. In either case, this configuration can be visualized as a central core surrounded by hosts.

The challenge with this type of configuration is that the size of the fabric is limited by the number of ports provided by the switch. A solution may be to join two switches together through a single connection. As this would be a link between switches and not between switches and a host, it is referred to as an Inter-Switch Link (ISL). Additional switches and additional ISLs can be added to further expand the fabric.

While this is a valid configuration, there is a fundamental flaw in this approach—limited bandwidth between switches.