The ultimate Leica bokeh is supposed to come from the pre-aspherical 35mm Summicron, but that's a bit weird; a 35mm has sufficient DOF that you rarely get anything far enough OOF to benefit.
Interestingly any focal length lens has the same DOF with the same aperture and the same SUBJECT magnification. That is if you take a picture with a 35mm and a 60mm lens so that the subject fills the same area of the frame (35mm lens will be at 1/2 the distance of the 60mm), and at the same aperture, then the DOF will be the same.
However, the background on the 60mm image will look softer, because the narrower field of view effectively expands half the amount of background to fill the frame - and hence also expands the blurred area of background making it look less "busy"
That's what you'd think, logically, but in fact, no it doesn't work like that.
Yes it does - here is an explanation better than anything I can conjure up....
Depth of field
Or if you like - bang in the figures to practically any DOF calculator you care to find.
All you need to know about depth of field is that it depends on the physical size of the objective lens. If you look at an f2.8 telephoto lens, it has a big piece of glass at the front. An f2.8 wide angle lens looks like a pinhole by comparison. That is because the wide angle lens is gathering light from a broader area, so needs less glass to get that same value of light.
As the size of the film or sensor increases it needs more light, to acheive the same f value. So the objective lens has to increase in size. It's not the f number that changes DOF but the diameter of the objective lens. This is why the cost of cameras and lenses rises exponentially as the format size increases, everything becomes more critical in terms of focusing and exposure due to the size of the glass required, which costs more to get right, and is easier to get wrong, all the way up to the Hubble telescope.
The bigger the piece of glass on the front, the shallower the depth of field with it wide open.