How to write more than 25 items/rows into Table for DynamoDB?

I am quite new to Amazon DynamoDB. I currently have 20000 rows that I need to add to a table. However, based on what I've read, it seems that I can only write up to 25 rows at a time using BatchWriteItem class with 25 WriteRequests. Is it possible to increase this? How can I write more than 25 rows at a time? It is currently taking about 15 minutes to write all 20000 rows. Thank you.