for my case, applying B1, can the current employer issue the inv

Thanks for your quick response!

For my case, applying B1, do I need business invitation letter to apply B1? Does the letter from my current employer work fine or I have to get business invitation letter from other company than my current employer? 

I have relative in the U.S, is it easy for me to apply B2 than applying B1 (business)? Which one takes better chance to get B visa approval? Do I also need invitation letter from my relative too if I apply B2?

how to write the B1/B2 invitation letter? what reason should be used?

Thanks very much for your help!