parquet-hive/parquet-hive-storage-handler/src/main/java/org/apache/hadoop/hive/ql/io/parquet/convert/HiveSchemaConverter.java
private static GroupType convertStructType(final String name, final StructTypeInfo typeInfo) {
    final List<String> columnNames = typeInfo.getAllStructFieldNames();
    final List<TypeInfo> columnTypes = typeInfo.getAllStructFieldTypeInfos();
    return new GroupType(Repetition.OPTIONAL, name, convertTypes(columnNames, columnTypes));

  }
private static GroupType convertStructType(final String name, final StructTypeInfo typeInfo) {
    final List<String> columnNames = typeInfo.getAllStructFieldNames();
    final List<TypeInfo> columnTypes = typeInfo.getAllStructFieldTypeInfos();
    return new GroupType(Repetition.OPTIONAL, name, convertTypes(columnNames, columnTypes));

  }
An optional group containing multiple elements