The Allbirds Tree family and the Wool family fit differently given their material makeups. The Tree shoes are made from lyocell (commonly referred to as "Tencel"), while the Wool shoes are made from merino wool.
Wool will naturally stretch over time, while the Tree retains shape. Please note if you have a wider foot or are in between sizes, we'd suggest going up to the next full size in each silhouette.
If you're normally a full size, we suggest sticking with that size in all styles :)