How to get the names of all keys of all levels in a Mongo Collection using Aggregations

Question

I want to get all levels of keys from a Mongo collection using aggregation. Let's say I have a collection with the below docs:

[
   {
      "t1":4,
      "t2":"test",
      "t3":{
         "t4":"test1",
         "t5":{
            "t6":"test2"
         }
      }
   },
   {
      "t1":5,
      "t100":"test3",
      "t3":"test4",
      "t4":{
         "t5":100
      }
   }
]

Required result: ["t1","t2", "t100", "t3", "t3.t4", "t3.t5", "t3.t5.t6", "t4", "t4.t5"]

Can anyone help me with this? Tried the below but it is not giving me all the nested keys in the documents. https://www.objectrocket.com/blog/how-to/get-keys-mongodb-collection/