Time complexity of creating a Hashie::Mash object

I want to understand how expensive is to create a new Hashie::Mash. Does calling Hashie::Mash.new(object_hash) creates a deep copy of the "object_hash"

Example: What is the time complexity of below given array size is M and emp object has N key value pair.

array.map { |emp| Hashie::Mash.new(emp)

Will it be O ( M x N ) ?

Note: I am trying to understand this from the performance perspective and N can be large won't be constant because of the nested hash. In case you want to look at the structure of emp ( employee which can have nested employees is)

{
"id"=> 1,
.
.
"nested_employee" => [

   {
    "id"=> 12,
     .
     .
   },
    {
    "id"=> 13,
     .
     .
   }]
.
.
}