When they get older their distinctive bark is a giveaway.  As a sapling, you’ll have to ID it by the leaf.  This can be tricky since it resembles a maple leaf although it is larger than a maple leaf.  Perhaps the is a mature sycamore nearby that you can pluck a leaf from to match up to the sapling in question.    Here’s a couple of links that may help you:

https://oplin.org/tree/fact%20pages/sycamore/sycamore.html

https://www.extension.iastate.edu/forestry/iowa_trees/trees/sycamore.html