Is it continuous? Is the material linear-elastic for small strains? Does it act as a cantilever beam when subjected to wind and other (e.g., earthquake) lateral forces? If so, you may solve it by writing the 2nd moment of area as a function of height ( I = I(x)), assuming a deflected shape (polynomial or trig series sum), and solving the beam deflection with Ritz or Galerkin method. Alternatively, just model it in finite element software.
For a composite beam (stepped I values along length), calculate local bending deflection in each piece, local rotation in each piece, rotation at the bottom, rotation at the top, deflection at the bottom, deflection at the top- work your way up. It's not just y1 + y2.
For the cone, you can assume a stress distribution similar to a cylinder and calculate moment, strain, and rotation along the length to find an average I. Using I at the small end should be conservative, using I at the large end should be unconservative.
Shear deflection may be significant as well, depending on diameter.
