The workman is specifically part of the cutting down of the tree with the axe, though.
That's true. But, again, they're talking about the making of idols. Here's the whole passage:
Jeremiah 10:2-10 said:2 Thus says the LORD:
“ Do not learn the way of the Gentiles;
Do not be dismayed at the signs of heaven,
For the Gentiles are dismayed at them.
3 For the customs of the peoples are futile;
For one cuts a tree from the forest,
The work of the hands of the workman, with the ax.
4 They decorate it with silver and gold;
They fasten it with nails and hammers
So that it will not topple.
5 They are upright, like a palm tree,
And they cannot speak;
They must be carried,
Because they cannot go by themselves.
Do not be afraid of them,
For they cannot do evil,
Nor can they do any good.”
6 Inasmuch as there is none like You, O LORD
(You are great, and Your name is great in might),
7 Who would not fear You, O King of the nations?
For this is Your rightful due.
For among all the wise men of the nations,
And in all their kingdoms,
There is none like You.
8 But they are altogether dull-hearted and foolish;
A wooden idol is a worthless doctrine.
9 Silver is beaten into plates;
It is brought from Tarshish,
And gold from Uphaz,
The work of the craftsman
And of the hands of the metalsmith;
Blue and purple are their clothing;
They are all the work of skillful men.
10 But the LORD is the true God;
He is the living God and the everlasting King.
At His wrath the earth will tremble,
And the nations will not be able to endure His indignation.
Again, the passage is contrasting idols, which are made by humans and cannot move or act on their own, with YHWH, who is the living God. Because the "workmen" is the only mention in that set of versus to carving, it's at least possible that the idol in question was a decorated tree -- but there's no reason to believe that that's what the idol looked like, and the passage doesn't require it. Wooden idols were carved out of trees, which was the point that the Scripture was making. The point is addressed directly in verse 8 before he moves on to make a similar point with metal idols (verses 9 and 10).