This morning I started thinking about how you might map a tree that is basically a country.
The above picture is a diagram of a tree which stands in my garden.
All the major branches and the trunk are interconnected, on a tree. Anybody can travel between them if they are capable of moving along those branches. But then once you get away from the major branches there are vastly complicated networks of smaller branches and twigs that it would be impossible to actually map.
It makes more sense, then, to divide the tree up into zones. Away from all the major branches radiate networks, which are the different zones marked A, B, C, D, and E. (F is a separate zone where there used to be a big branch, which fell off.)
The red arrows are an attempt to illustrate depth - if the arrow is pointing down it indicates that the branch sort of comes back towards the viewer and if the arrow is pointing up it indicates the branch sort of points away. No arrow indicates the branch is side-on.
Then within each zone there are 4 sectors. Where sectors overlap with each other (A2 and B3, C4 and B2, C2 and D1, C3 and D3, and D4 and E1) travel between zones is possible by going between leaves and twigs in the different zones.
Within each sector there is no need to map anything - you just need to make a note of what is in each sector. It is presumed that there are ways of travelling within sectors fairly straightforwardly, because people will have built up ropeways, spider-silk bridges and whatnot to allow interconnectedness. So if you are in A2 you may have to travel for a day to visit the wizard who makes his home on a certain twig in A3, but you can do it.
All zones and sectors connect with what is called the outer canopy, which is obviously the outer bit which is all leaves, buds, and the very thinnest narrowest twigs. Out there it is probably impossible to build anything because of wind and rain and because of the activities of giant forest animals. Adventurers willing to risk that danger can go out into the outer canopy and use it to traverse the tree if they desire (for example from E3 to A3), but doing so will incur a huge risk.
I have no idea whether this would work or not in a game.