Nested object within nested object annotation question

[johntadd]

Following

https://www.elastic.co/guide/en/elasticsearch/guide/current/nested-objects.html
https://www.elastic.co/guide/en/elasticsearch/guide/current/nested-mapping.html

I create an index with nested object enabled.

Now I have a new question. When having a complicated doc whose nested object actually contain other arbitrary nested objects (that in turns may contain other arbitrary nested objects, and so on.). For instance

"level1": [
    {
         "level2": [
             {
                 "level3": [
                     { 
                          ...
                     },
                     ...  
                 ]
             },
             ...
         ]
    },
    ...      
]

In such case, do I need to specify "type": "nested" at each field at all level (For example, level1 annotated with "type":"nested", so do level2, level3, and so on)? Or the mapping only need to be specified with "type": "nested" at the level1 field?

Thank you.