num_level in Parquet Cpp library & how to add a JSON field?

[ivywuyzl]

Hi, 
I’m creating a parquet file using the parquet C++ library. I’ve been looking 
for answers online but still can’t figure out the following questions.

1. What does num_level mean in the WriteBatch method?
 WriteBatch(int64_t num_levels, const int16_t* def_levels,
                    const int16_t* rep_levels,
                    const typename ParquetType::c_type* values)

2. How to create a filed for JSON datatype?  By looking at this link 
https://github.com/apache/parquet-format/blob/master/LogicalTypes.md, it seems 
JSON is not considered as a nested datatype.  To create a filed for JSON data, 
what primitive type should it be? According to the link, it says “binary 
primitive type”,  does it mean "Type::BYTE_ARRAY”?
        PrimitiveNode::Make(“JSON_field", Repetition::REQUIRED, Type:: ?, 
LogicalType::JSON))
        
Any help is appreciated! 
Thanks,
Ivy