This need to be done recursively. The tree can be really huge. For this reason, you should not go through all of it at once. Only the nodes that are of interest should be expanded (browse into).
Note that QuickOPC provides controls and dialogs for UI browsing of OPC servers and nodes - they are not just in the demo app, they are exposed as components (for desktop UI, such as Windows Forms). So, for the common cases, you do not need to do develop the dialog windows yourself.
I need to browse opc ua server for all nodes, tags, etc, and create tree of them. Just like in your demo application where after clicking browse data i get window with all folders, data and node information for server. I need to make such window by myself. Is it possible to get all that data as some collection form opc at once, or I have to recursively browse all tree nodes one by one.