Mongodb Batch Insert Using Aggregate Not Working

[Site Register]

Hi All,
It tried to batch insert by leveraging aggregate. Somehow it only inserted one 
record for each batch. Very appreciated if you can help.
from(fromFile)
 .split().tokenize("\n",1)
 .aggregate(constant(true), new ArrayListAggregationStrategy())
 .completionSize(1000)
 .completionTimeout(500)
 
.to("mongodb:mongoBean?database=databaseName&collection=collectionName&operation=insert");

Thank you,