I have a json file like this:

{
    "parent1": {
        "child1": "bob"
    },
    "parent1": {
        "child2": "tom"
    },
    "parent2": {
        "child1": "jon"
    }
}

I want to merge the values present under duplicate toplevel keys. So the expected output should be:

{
    "parent1": {
        "child1": "bob",
        "child2": "tom"
    },
    "parent2": {
        "child1": "jon"
    }
}

Currently I am using the following code to check duplicate keys:

import json

def check_duplicates(pairs):
    d = {}
    for key, val in pairs:
        if key in d:
            raise ValueError(f"Duplicate key(s) found: {key}")
        else:
            d[key] = val
    return d

filename = "test.json"
with open(filename, "r") as f:
    try:
        data = json.load(f, object_pairs_hook=check_duplicates)
    except ValueError as err:
        print(f"{filename}: Failed to decode: {err}")

Any idea how I can merge them?