Even though your project only consists of Sheets, Notes in Sheets and Attachments to Notes, you can create an infinitely 'deep' network of Notes and Relations in many dimensions, and still structure it according to your views.
Your project tree is not your network. Your network is the cumulation of all your Concept Maps or Mind Maps. These you create on Sheets, or rather Sheet windows, from Notes and Relations. Each Note is visualized as a 'Yellow' and contains all information for that Note, including Attachments to external documents and internet pages, Relations to and from other Notes, annotations and an engine to jump to related Notes. Relations are visualized as lines on the Sheet windows.