Serializes the this for later deserialization via deserialize.
No guarantees are made about the format used other than that the same version of GTK will be able to deserialize the result of a call to serialize and deserialize will correctly reject files it cannot open that were created with previous versions of GTK.
The intended use of this functions is testing, benchmarking and debugging. The format is not meant as a permanent storage format.
a Bytes representing the node.