The Lewis diagram is therefore There are five electron pairs around the selenium atom. The electron pair geometry is therefore trigonal bipyramidal. However, one of the electron pairs is nonbonding. The nonbonding pairs occupy more space. If we place this nonbonding electron pair in one of the axial positions, it has only three neighbours rather than the four it would have if it were in an equatorial position.
Xenon has eight valence electrons.
The Lewis diagram is therefore There are four bonds plus the nonbonding electron pair, for a total of five groups of electrons. The electronic geometry is therefore trigonal bipyramidal. Again, the nonbonding electron pair likely occupies an axial position so the molecular shape is trigonal pyramidal. It is difficult to predict which of the other atoms occupies the other axial position.