Arbitrary nested tree hierarchy data model

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Not sure if this is the right place to ask, but we are trying to model a 
user-generated tree hierarchy in which they create child objects of a 
root node, and can create an arbitrary number of children (and children 
of children, and on and on).  So far we have looked at storing each tree 
structure as a single document in JSON format and reading/writing it out 
in it's entirety, doing materialized paths where we store the root id 
with every child and the tree structure above the child as a map, and 
some form of an adjacency list (which does not appear to be very viable 
as looking up the entire tree would be ridiculous).

The hope is to end up with a data model that allows us to display the 
entire tree quickly, as well as see the entire path to a leaf when 
selecting that leaf.  If anyone has some suggestions/experience on how 
to model such a tree heirarchy we would greatly appreciate your input.