With the Binary Search Tree shown below, what is the sixth node visited using a pre-order traversal

Please show steps clearly

What is the most popular application of in-order traversal in binary search trees?

When presenting a menu option to the user in the main cpp file. Asking user to input in an ID, how do I code a search method implementation where it takes that ID and search it in the binary tree and either return true if found and false if not. I am trying to steer away from using item which is attached to both (ID, username). I am trying to only take the ID input and the node pointer and traversing through the binary tree to find if the ID matches any of the nodes.