/summon villager ~ ~2 ~ {VillagerData:{profession:librarian,level:5,type:plains},Offers:{Recipes:[
{buy:{id:melon,Count:16},buyB:{id:pumpkin,Count:32}
,sell:{id:pumpkin,Count:1,tag:
{display:{Name:"{\"text\":\"Melonpkin Upgrade\",\"color\":\"dark_green\"}"}},maxUses:128}}]}}