URL GET parameter representing and parsing embedded objects

I'm working on an API that consists of several collections that have relations to each other. I want to give users the opportunity to eagerly fetch records from associated collections via a GET url parameter.

For instances

/api/clients/

Would return an array of objects, each representing a client.

But clients have "employees" and "templates". "Templates" also have "revisions." And lastly, "revisions" have "groups"

My strategy for the format of the url parameter is something like this:

/api/clients?expand=[employees][templates[revisions[groups]]]

Which represents:

clients
 + employees
 + templates
   + revisions
     + groups

My question is, what is a good way to go about parsing a string in this format: [employees][templates[revisions[groups]]] to arrive at an object like this:

{
  "employees": {},
  "templates": {
    "revisions": {
      "groups": {}
    }
  }
}

Or something similar that's easy to work with. I'm working in NodeJS so any answers specific to that environment are a plus. Regex?

Going off @Kovge 's suggestion, I'm going to handle this situation with a JSON string passed in my URL get request. It's a bit verbose, but should be acceptable.

Here's how I'd represent my eager-fetching associated collection records:

[
  {
    "resource": "employees"
  },
  {
    "resource": "templates",
    "extend": [
      {
        "resource": "revisions",
        "extend": [
          {
            "resource": "groups"
          }
        ]
      }
    ]
  }
]

Basically using arrays of objects with "resource" parameters and optional "extend" parameters. My request will end up looking like this: (url encoded)

http://example.com/api/clients?extend=%5B%7B%22resource%22%3A%22employees%22%7D%2C%7B%22resource%22%3A%22templates%22%2C%22extend%22%3A%5B%7B%22resource%22%3A%22revisions%22%2C%22extend%22%3A%5B%7B%22resource%22%3A%22groups%22%7D%5D%7D%5D%7D%5D

EDIT:

This is what my result ended up looking like, still playing with things. enter image description here