He has signed up for the Woodland Trust's Jubilee Woods campaign to commemorate the monarch's reign. "Royal fever starts here. The trust wants to plant six-million trees to mark the Queen's 60 years on the throne," said O'Leary.
"Everyone should have access to trees and the benefits they provide for health, well-being and wildlife. This can only happen with everyone's help."
Jubilee Woods is the trust's most ambitious project to date. Trees will go into community spaces such as parks and playgrounds. Princess Anne is the project's patron.
Community groups can order free tree packs, which contain a sapling grown on one of the royal estates, said Victoria Hodson, project manager at the trust.
The trees will support wildlife such as starlings, blackbirds and song thrushes. Register at www.moretreesmoregood.org.uk/jubilee.