To minimise the concentration of mould on the Christmas tree, it should be treated with a leaf blower or washed off with a very mild bleach solution, before bringing it inside the house. It has been found that a room containing a freshly cut Christmas tree for two weeks, has five times the normal level of mould present. This can cause allergic rhinitis and asthma symptoms for anyone in the house prone to allergic reactions.
It is better to use artificial trees and decorations over the festive season of there are people in the house with allergies. If you want to minimise the risk of airborne spores and mould irritating normal people, then only keep the tree inside for a week. Artificial trees and decorations can be dusty, especially if they have been in storage. These should be wiped clean before use, since the dust will also house spores and mould.