It's not at all obvious that it exists: http://www.washingtonpost.com/news/morning-mix/wp/2015/04/14....
More men may work in tech because on average men are more interested in the subject.
The key word in the preceding sentence is "may." "Bias" is complex and hard to prove and in the case of the tech industry there may be bias or there may not be. Even the phrase "tech industry" is odd. Does that include academic scientists? Where does tech end and other industries start? See also e.g. http://philip.greenspun.com/careers/women-in-science.