US President Donald Trump and French President Emmanuel Macron plant a tree warched by Trump's wfe Melania and Macron's wife Brigitte on the grounds of the White House April 23, 2018 in Washington,DC. Pic/AFP

The photograph was seen around the world: US President Donald Trump and France's Emmanuel Macron, gilded spades in hand, shovelling dirt over a young sapling. It was a symbolic gesture: the tree came from a northern French forest where 2,000 US Marines died during the First World War.