Trying to store object key(s) which as '.' in key string

I am trying to store object key(s) which as ‘.’ in key string as below,
“class”: {
“test. last. name 1.5.4”: {
“$numberLong”: “1736660733968”
}
}
When I try to store the data in above orders, which following dot notatio and creating a new child object and storing in mongodb. I tried using string literals, escape keys and few methods. Can anyone help me on this.