Step 1: In the Williamson synthesis, if a tertiary alkyl halide is used, elimination (E2) is more favored than substitution, leading to the formation of alkene.
Step 2: Therefore, a mixture of alkene and ether is obtained, with alkene being the major product.
Final Answer:
\[
\boxed{\text{a mixture of alkene as a major product and ether as a minor product forms}}
\]