The AudioProcessorValueTreeState is an optional class, that is intended to enhance the AudioProcessor’s handling of Parameters exposed to the host, as well as providing a public ValueTree member, where your additional parameters, that are not automated by the host (e.g. because they are of a kind the host wouldn’t understand, like in your case).
This makes it easy to serialise the plugin’s state in one go for the host to save and restore it later using getStateInformation and setStateInformation.
To use the AudioProcessorValueTreeState, create one member of this type in your AudioProcessor (this procedure is called aggregation).
The way, how the automated parameters are added was recently changed, have a look in this thread: “AudioProcessorValueTreeState Improvements”.
After that to add your own information to the state member of that AudioProcessorValueTreeState, like @Xenakios explained.