I would make it out of morphs.
But because it has to be oblique you cant pull the morph.
First draw the shape of the tree and rotate it vertically.
So I would make a frame of morphs and make the treads out of morphs or slabs.
Made a video of it.
I gave the shape of the tree no thickness.
Architectural construction designer, draftsman, modeller ArchiCAD 25.
Remember that the stair treads are always perpendicular to the baseline of the stair (new stair tool).
So create the stair so the baseline runs perpendicular to your treads and then edit she shape of the boundary of the stairs to get the shape of the flight that you require.
Barry.
One of the forum moderators. Versions 6.5 to 27 i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10 Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11