Swift version seems to be broken and crashes for any tree with more than one node due to an error in reading the input here:

let t = Int(readLine()!)!

for _ in 0..

root = tree.insert(root: root, data: Int(readLine()!)!)

}

The problem is that the 'for' loop expects for each node data to appear on a separate line, while they all on the same line separated by commas.