While VBA collection classes are best known for storing collections of single custom object types, they can also be built into much more complex data structures. This includes storing multiple object collections within a single collection class, permitting a node-like structure to store any number of related items.
A common object structure in VBA is the collection class, where many custom objects are grouped together. VBA also permits additional layers above the collection class, resulting in a collection within a collection. This is a useful technique for organizing hierarchical data or grouping certain objects.