Butternut squash and Pumpkin belong to the same family and are similar to each other.
But butternut squash and pumpkin are different and taste different so when you need to use butternut squash in a recipe you should use butternut squash and when the recipe calls for pumpkin you should use pumpkin.
I have made some butternut squash pie and it turned out pretty good but it didn't taste like pumpkin pie so if you want pumpkin pie you should use pumpkin pie.
But I would highly recommend you trying some butternut squash pie as in my opinion the butternut squash pie is delicious.
The taste of butternut squash is somewhat similar to pumpkin but it does have a different taste.
Butternut squash has a sweet nutty taste that is a bit different than pumpkin and also butternut squash has a tan, yellow skin and orange fleshy pulp with a compartment of seeds in the bottom.