Physically, it's a mature tree with an inscribed  metal band  suspended at mid-canopy height and mid-canopy radius.

There are 10 of them dotted around the park.   The trees are of different species.

They were installed as the Olympic Park was being finalised as an art project.   

Diamond Geezer found them all last month and documented them here:  https://diamondgeezer.blogspot.com/2020/05/history-trees.html

The official artist's page is here: https://www.ackroydandharvey.com/olympic-commission/   but it seems that the species names on it are incorrect.

OSM nodes 5705465172, 4428021487 and 4428021486 represent some of the History Trees.   There seem to be 4 'missing' from the map.