Well. I've solved it as rename filed sections to parts:
case class Template(name: String, marks: List[Mark], sections: List[Section])
case class Mark(name: String, description: String, index: Int, indexTree: String, dataType: String, rate: Int)
case class Section(name: String, index: Int, indexTree: String, marks: List[Mark], parts: List[Section])
Collection:
{
"name": "Caption",
"sections": [{
"name": "Section name",
"index": 1,
"indexTree": "1",
"marks": [],
"parts": [{
...
"parts": [...]
}, ...]
}],
"marks": []
}