I’m not sure what type of weather you have had in Italy, but if it was anything like here, the tree is probably stressed from lack of water. If you want to grow the willow as a tree form it shouldn’t need pruning. Here is a great site about willows and willow pruning to check out.
Welcome! I’m Margaret Roach, a leading garden writer for 25 years—at ‘Martha Stewart Living,’ ‘Newsday,’ and in three books. I host a public-radio podcast; I also lecture, plus hold tours at my 2.3-acre Hudson Valley (NY) Zone 5B garden, and always say no to chemicals and yes to great plants.