The idea

With each ticket 2 trees are planted to bind the CO2 emissions for the visit of an event – concert, music festival, stadium visit, museum visit, folk festival, … – within one year.

How effective this can be is illustrated by the following example of a “football fan”:

Almost 60,000 trees would have to be planted to offset the CO2 emissions of a match day of the 1st Bundesliga (in 10 years).

https://www.deutschlandfunk.de/serie-endspiel-ums-klima-1-klimasuender-fussballfan.1346.de.html?dram:article_id=437166

But what if you plant two trees per ticket?

In the 2017/18 season, an average of 394,911 spectators per matchday came to the stadiums (https://www.dfb.de/bundesliga/statistik/zuschauerzahlen/). Then almost 790,000 trees would be planted per matchday. This would correspond to an area of over 631 football pitches. The emissions of a matchday would be tied up in 12 months.

If we add the 2nd and 3rd Bundesliga, football alone would make it possible to plant over a million trees per match day.

The cost for each individual would be only 2€ per match day – a small amount personally.