Pine and fir trees are not toxic. However, the needles from pine trees and artificial trees are sharp and can cause trauma, if ingested. Cedar contains irritants and should not be used. Decorations made of plastic such as some angel hair, tinsel, spray snow and ornaments are non-toxic. However, injesting pieces of them can cause blockage of the intestinal tract.
Some angel hair is made of fiberglass which is very dangerous if eaten.
If you use a spray-on decoration, keep your birds away while you spray. Some of the propellants contain freon. Glass and metallic ornaments and lights hung on Christmas trees can be broken. The sharp edges can cause cuts, both externally and internally. Bubbling light fluid contains a toxic solvent which irritates eyes.