Using `networkx.readwrite.json_graph.tree_data` does not preserve Graph attributes

When using networkx.readwrite.json_graph.tree_data to returns data in tree format that is suitable for JSON serialization and then convert this data back using networkx.readwrite.json_graph.tree_graph, you lose the Graph attributes.

Current Behaviour

For example the following is the current behaviour

>>> import networkx as nx
>>> from networkx.readwrite import json_graph
>>> DG = nx.DiGraph(page="some text")
>>> DG.add_node(5434)
>>> print(DG.graph)
{'page': 'some text'}
>>> data = json_graph.tree_data(DG, root=5434)
>>> DG = json_graph.tree_graph(data)
>>> print(DG.graph)
{}

Expected Behavior

I should get the following

>>> DG = json_graph.tree_graph(data)
>>> print(DG.graph)
{'page': 'some text'}

Environment

Python version: 2.10
NetworkX version: 2.6.3

Start with the networkx.readwrite.json_graph.tree_data and tree_graph entry points and reproduce the provided round-trip example. Add a regression test showing that graph attributes survive conversion, then run the relevant JSON graph tests and confirm the reconstructed graph retains {'page': 'some text'}.