Load firebase structure from a collection within a document

How do I…

Load firebase document that contain another collection

What is the expected result

I wish to load a document in Firebase that contains a collection

What is the actual result

I reach to make it work on a basic level :
Collection > Document

But here i have database structure like this :
Collection > Document > Collection > Document

And when i use the get document function it returns an empty structure

Any thoughts ?

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