My day care is on my main level which is open plan. So there has always been a number of items that they may not touch. They can't pull the books from the bookshelves and similar. Maybe because children here have been taught what they can and cannot access, I've never had an issue with the tree or decorations. I few inquiring steps each year and a simple instruction that they may look but not touch, is all it's ever taken.
My biggest hurdle has always been keeping the damn cat out of it. The children think it's hilarious that she climbs up inside the tree maybe more so because they understand it's a no-go zone and so she's being really naughty.