Copy directory from system to pendrive (regular 2.0 USB device) using C# code

There is no "fast copy" method that will guarantee to make a significant improvement in transfer speed, you are almost certainly limited by three factors:
1) USB transfer speed - this will depend on the version of USB for both the port on the computer and the version of USB in the pendrive - the lowest version of the two controls the USB speed. USB1 had a maximum transfer rate of 12Mbits per second, or about 1.2 Mbytes per second; USB 2 took that to a maximum of 480Mbits per second - but you may not achieve that maximum or even anywhere near it depending on the quality of your kit and drivers.
2) Pen drive write speed: I've seen some older / cheaper ones that struggle to keep up with USB1!
3) Size of files: more small files will take longer to transfer (and probably will take more space) than the same nGB of fewer large files.

There is no magic bullet here: you have bottlenecks and you need to identify them - there is no software algorithm that can vastly improve the transfer time.