While there is a Web component block to decode a JSON string into a tree of name-value pairs, there is no native block support to reverse this.
I've attached a rudimentary blocks routine to make a JSON string out of a pair list, and sample calls.
Look into the experimental FireBase component if you want to live in a persistent JSON tree.
I have an incomplete Rock Paper Scissors sample I started if you want a head start on FireBase.
See the end of this page for how to navigate a tree in AI2 ...
ABG