Here's the tutorial...
Make a sketch on the front plane as shown
Set the top spline handle to horizontal and bottom spline handle to vertical.
Make the spline rotate around the axis to get the shape of a bulb. Then change the transparency.
Add a plane with reference to the top plane. You can name this as the "twisting plane".
Draw a line on the right plane and make it co-incident withe the newly created plane (twisting plane)
Add a sketch on the "twisting plane",set it at 45 deg to the right plane as shown and then sweep it.
Insert->features->move/copy->rotate the feature around y axis by 180 degree.
Intersect all the three and then hide the unrequired parts.
Make the top portion of the spline by creating spline on surface.
tools->sketch entities->spline on surface
make the middle point of the newly created "spline on surface" co incident with the temporary axis. But before sure to delete the automatically created centre and the "on surface" relation of the middle point of the spline.
make the bottom splines by joining the helical spline and the base. Add a equal curvature relationship between both and set the base handle of the spline "along y axis". Then exit the sketch.
Draw a circle on the base plane. But before be sure to find out the minimum radius of the 3d sketch by right clicking on the spline sketch and choosing "show minimum radius".
Choose the circle and the bottom spline joining the base and set a "on pierce" relationship which is just below the "co-incident" relationship on the left pane. Then sweep the profile through the 3d sketch created and then hide the part shown in blue to get the tube. U may change the spline points according to your minimum radius requirement.