Multiple schemas per collection

Hello, let say I have a collection where a data structure have the following view:

{
  "_id" : "puAy4j4KnNNRpKGzW",
  "title" : "Some category",
  "type" : "category",
  ...
},
...
{
  "_id" : "aF7GZh4k3TZHiBqpk",
  "title" : "Some product",
  "type" : "product",
  ...
},
...
{
  "_id" : "3amLTwhsDYue4qJYW",
  "title" : "Some product variant",
  "type" : "variant",
  ...
},
...
{
  "_id" : "M9H35NXTmuSyKPtA2",
  "title" : "Some variant option",
  "type" : "option",
  ...
}

each type of doc has its own unique fields, also there is a common fields for all types. To manage that collection2 and simpleschema are used.

My question is how to build schema for such kind of pattern?