Num of segments in index

While optimizing it's pretty easy to determine a number of segments by executing Optimize command with max_num_segments parameter.
My question is about indexing prior to optimizing, though.
I checked the section and I still couldn't find - how do I control the number of segments during indexing? Is there a simple way to tell to ES that I am willing to pay with indexing time and frequent merges but keep number of segments below 10, for example?

Thanks in advance,