Hi there hope i can be of assistance.
The most common cause of this is the front wheels or tires.
If these are slighlty buckled, or older tyres these can cause an imbalance. This at speed, then translates as vibration through the steering wheel.
So first have all 4 tires/wheels balanced.
Also, have a detailed inspection of the front suspension system. Its unlikly to be a bushing problem, but its better to be safer than sorry.