This requires you to research all packages for one of your tanks, and also to research any and all tanks that are the next higher Tier and are shown on the right end of the packages screen. Since Tier 1 tanks already have all their packages researched, all you have to do is get enough tank XP to research all the Tier 2 tanks for that nation. 2 good games should be all you need for enough XP, although amounts vary a lot!
You do not have to buy all the upgrades or next tanks, you just need to get enough tank XP on that tank to research all the upgrades and next tank.
At time of writing(August 1st, 2015), the Chinese tank tree will give you this achievement after researching only 1 tank as there is only 1 tank line!