Where does “insessio” come from?

insessio (Latin) comes from Latin insidere, from Latin īn-, from Latin în, from Latin en, from Proto-Italic en, from Proto-Indo-European h₁én — in.

Ancestry of “insessio”, step by step

Step	Language	Word	Meaning
1	Latin	insidere	present active infinitive of īnsideō;...
2	Latin	īn-	un-, non-, not
3	Latin	în	in, at, on, upon, from (space)
4	Latin	en	lookǃ beholdǃ; reallyǃ?; come onǃ
5	Proto-Italic	en	in
6	Proto-Indo-European	h₁én	in