  Tungsten ditelluride WTe$_2$ is a type-II Weyl semimetal with electronic
properties highly sensitive to external pressure, as demonstrated by the
superconductivity emerging under pressure. Here, we study the optical
conductivity of the type-II Weyl semimetal WTe$_2$ under external pressure at
room temperature. With increasing pressure, a pronounced spectral weight
transfer occurs from the high-energy to the low-energy interband transitions,
with drastic changes in the profile of the optical conductivity spectrum
indicating a high sensitivity of the electronic band structure to external
pressure. The detailed analysis of the pressure-dependent optical conductivity
furthermore reveals anomalies at the pressures $\sim$2 and $\sim$4.5~GPa, where
an electronic and a structural phase transition, respectively, were reported in
the literature.
