So here are 2 screenshots from US West and Europe servers showing 2 different guilds gathering at the Guild Tree to chat, have fun and get the benefits for 15 minutes.
(sorry my recording software toolbar is covering the server name, but my level 46 mage is in US west and level 42 warrior in Europe)
Gathering for the Guild Tree US West - Russians
Gathering for the Guild Tree US West - Sanctum
and also here is a movie about it Wartune Guild Tree Event and Explanations