Realistic Christmas trees suitable for several scales, including common dollhouse and railway scales, can be easily made using preserved branches of lycopodium also known as prince's pine,princess pine or erica moss a sustainably harvested form of club moss available over the internet, by mail order, or through dried floral supply outlets. This tree was created from a kit available in the UK through the Cancer Foundation as a fundraiser at dolls house fairs. Trees made from lycopodium will last a long time if properly cared for. Our family just recently refurbished some used in a table top Santa decoration from the 1920's.
To make your tree ultra realistic (for a model railroad or Christmas village) you can add some tiny cones as well.