A top-level page that you would like to act as a "Collection" of instances is typically achieved creating an instance of Code-Pega-List and populating the .pxResults page-list property with the items in your Collection.

Try as best you can stay in rules to append to your Page Lists. 

Should you need to step into Java, my advice would be to configure something that appends to a Page List in a sample Data Transform or Activity in Dev Studio [e.g. using .pxResults(<APPEND>)], then use "View Java" from the Actions menu to review what Java code Pega generates, from where you will learn how to work with the ClipboardPage and ClipboardProperty objects to achieve what you need to.