I’m not sure the two should be intrinsically linked like this.
AudioProcessorGraph has a very specific purpose, to connect AudioProcessor instances together in a “graph”.
A ValueTree is more of a data structure. You could define ValueTree types and properties to relate to a specific configuration of an AudioProcessorGraph but it’s unlikely there will be a one-fits-all solution for this. It will depend hugely on the abilities of your app and what types of AudioProcessors you support etc.
I fear that any forcing of AudioProcessorGraph in to a ValueTree context would be essentially the same as the ComponentBuilder class. I think this is now largely viewed as a bit of a failed experiment: Is anyone using the ComponentBuilder class?
This isn’t to say that you shouldn’t use ValueTrees and AudioProcessorGraphs in combination however, they would be very complimentary. I just think you’re probably better of rolling your own AudioProcessorGraph builder based on your specific ValueTree structure, it’s probably not something generic enough to go in to the JUCE library (but it might make an interesting tutorial or demo!)
However, I’m not a big expert in AudioProcessorGraph so it could be that it boils down nicely to a 1:1 ValueTree representation, these are just my initial thoughts…