Un train peut en cacher un autre

This is the warning sign on every level crossing in France. For non-French speakers it means “one train might conceal another [coming the other way, so look before you leap]”.

Here it’s un arbre peut en cacher un autre. Look carefully and you’ll see the main tree has, nestling within it, another completely independent little tree. They must once have been seedlings together, but one grabbed all the nutrients and grew big and strong. Meanwhile sibling tree snuggles within the bark of the biggie.