Can I get a visa to cover two visits 13 months apart and what paperwork

From UK. : I have a visit 20-28 October to Beijing - work (but not trade, as a charity) plus conference; I have letter of invitation to match these dates. However, I then will have another trip a year later - likely to be 23-36 October. Question 1: how is a 1 year visa calculated - if it's between two arrival dates this is over 1 year? Question 2: And if it is over one year, then what are my options? I can't see a two year option. Question 3: So do I need a five year option? Question 4: If so, do I need additional paperwork? If so, what? Question 5: should I tick F or M Thank you.