The variable type that allows that type of input is called a "value table." An easy thing to do is right click on the Union tool in Modelbuilder, go to Make Variable > From Parameter, and add the "Input Features" as a variable. Right click on the Input Feature variable, make it a parameter, and you'll have your input value table when you open up the model as a geoprocessing tool.
The variable type that allows that type of input is called a "value table." An easy thing to do is right click on the Union tool in Modelbuilder, go to Make Variable > From Parameter, and add the "Input Features" as a variable. Right click on the Input Feature variable, make it a parameter, and you'll have your input value table when you open up the model as a geoprocessing tool.
