Here are some options depending on the context:
Formal/Botanical:
* Pinheiro-do-natal (abeto): This is the most accurate translation, using the specific scientific name for spruce ("abeto") in Portuguese.
* Árvore de Natal de abeto: Literally "Christmas tree of spruce."
* Pinheiro-do-natal da espécie abeto: "Christmas tree of the spruce species."
Informal/Common:
* Pinheiro-do-natal: This is the most common way to say "Christmas tree" in Portuguese. While it doesn't specify the type of tree, it is widely understood to refer to the traditional spruce.
* Árvore de Natal: "Christmas tree," again, without specifying the type.
You can also use the word "abeto" on its own, which is understood to be a Christmas tree in Portuguese.
Ultimately, the best way to say it depends on your specific context and the level of formality you want to achieve.