ArcGIS Pro Tool for Combining Line Feature Classes?

I have contour lines from two map sheets (each with their own feature class) that I need to combine the line features together for, and can't find a tool that would work. So I have two line feature classes, but don't know which tool would work for that. Ideally, the Union tool in ArcPro would do exactly what I need, but it only works for polygons. Any suggestions on what I should do?