presentation nodes

node trees are used to hold lots of data, like Collections, Triumphs, Catalysts, Metrics, Medals, etc.

they're a hierarchical structure where each branch node can have multiple children.
a node's children can be other presentation nodes, collectibles, metrics, craftables, or records (triumphs)

an example:

                                      PresentationNode
                                         Collections
                                       ↙            ↘
                            PresentationNode      armor, mods,
                                "Weapons"          flair, etc
                              ↙           ↘
                   PresentationNode       special,
                       "Primary"         heavy, etc
                    ↙             ↘
          PresentationNode      sidearms, bows
           "Hand Cannons"      auto rifles, etc
          ↙              ↘
  Collectible           some other hand
"Kindled Orchid"      cannon collectibles

root nodes

many of the top level nodes are available through the destiny2CoreSettings key in the settings endpoint's data

if you want to enumerate collections data, instead of hardcoding 3790247699 in your app, just load the current d2 settings and check the value of collectionRootNode

there's lots of these, including node hashes for collection, badges, records, medals, metrics, activeTriumphs, activeSeals, legacyTriumphs, legacySeals, medals, exoticCatalysts, lore, crafting