I did try this (varying by color, not size) but it is a little iffy working with discrete values instead of continuous ones. I made Attribute 2 a short integer datatype and used the Color option of "Vary symbology by attribute".
Then I made a discrete color scheme with 6 colors to match to the 6 domain values of the attribute. But when I do this, the color scheme breaks up the possible values into 3 "ranges" (see screenshot). I'm not sure why there are only 3, if I could create 6 ranges I could maybe map them to the 6 values, but I can't seem to figure out how to change the number of value ranges. Ideally I could simply map one color to one value and not have any ranges at all.
Below you can see the the 3 ranges on the left in the Contents panel the range sliders in the Symbology panel on the right.
