A (16) Moreover, thou son of man, take thee one stick, and write upon it, For Judah, and for the children of Israel his companions:
B (16) then take another stick, and write upon it, For Joseph, the stick of Ephraim, and for all the house of Israel his companions:
C (17) And join them one to another into one stick; and they shall become one in thine hand.
B1 (18,19) And when the children of thy people shall speak unto thee, saying, Wilt thou not shew us what thou meanest by these? Say unto them, Thus saith the Lord GOD; Behold, I will take the stick of Joseph, which is in the hand of Ephraim, and the tribes of Israel his fellows,
A1 (18) and will put them with him, even with the stick of Judah, and make them one stick, and they shall be one in mine hand.
You might be able to split up parts A more, like this:
A(16) i: Moreover, thou son of man, take thee one stick, and write upon it,
ii: For Judah,
A1: (18) i: and will put them with him, even with the stick of Judah,
ii: and make them one stick, and they shall be one in mine hand.
Given that the word “stick” occurs throughout the passage I don’t think it forms part of the chiasm. I think my original submission highlighted only “Judah” and “Joseph / Ephraim”.