Hi Paul, There isn't a specific, prescribed way to add emigration and immigration information on Wikitree. The only place to put the info is in the Biography. The main point is that you have a source for what you say.
If possible, I include both the emigration info, which sometimes includes different information, as well as the immigration info, including sources for whatever I find. To back up what I say about immigration, I will include a link to the ship's manifest, if I can find it, as well as citizenship papers that give the info about the date and ship of immigration. For a Swede, I will also include whatever reference I can find in the parish registers showing that the emigrant "checked out" with his priest before he left.
I am a nautical type, so I will also include as much info as I can get about the ship (length, age, type of propulsion, number of passengers), with a link to a picture, if I can find one. (My great grandfather came from Bremen to New Orleans in the middle of summer on a 90-100 foot sailing ship with about 200 others. The trip took 5 weeks. Glad I wasn't on that boat!)