The following information is excerpted from NFPA 1, Fire Code (2012 edition)
10.14 Combustible Vegetation
10.14.1 Combustible vegetation, including natural cut Christmas trees, shall be in accordance with Section 10.14.
10.14.1.1 Christmas tree placement within buildings shall comply with Table 10.14.1.1.
10.14.2 In any occupancy, limited quantities of combustible vegetation shall be permitted where the AHJ determines that adequate safeguards are provided based on the quantity and nature of the combustible vegetation.
10.14.3* Provisions for Fire Retardance for Artificial Vegetation.
10.14.3.1 Artificial vegetation and artificial Christmas trees shall be labeled or otherwise identified or certified by the manufacturer as being fire retardant.
10.14.3.2 Such fire retardance shall be demonstrated by each individual decorative vegetation item, including any decorative lighting, in an approved manner.
10.14.4 Vegetation and Christmas trees shall not obstruct corridors, exit ways, or other means of egress.
10.14.5 Only listed electrical lights and wiring shall be used on natural or artificial combustible vegetation, natural or artificial Christmas trees, and other similar decorations.
10.14.6 Electrical lights shall be prohibited on metal artificial trees.
10.14.7 Open flames such as from candles, lanterns, kerosene heaters, and gas-fired heaters shall not be located on or near combustible vegetation, Christmas trees, or other similar combustible materials.
10.14.8 Combustible vegetation and natural cut Christmas trees shall not be located near heating vents or other fixed or portable heating devices that could cause it to dry out prematurely or to be ignited.
10.14.9 Provisions for Natural Cut Trees.
10.14.9.1 Where a natural cut tree is permitted, the bottom end of the trunk shall be cut off with a straight fresh cut at least 1/2 in. (13 mm) above the end prior to placing the tree in a stand to allow the tree to absorb water.
10.14.9.2 The tree shall be placed in a suitable stand with water.
10.14.9.3 The water level shall be maintained above the fresh cut and checked at least once daily.
10.14.9.4* The tree shall be removed from the building immediately upon evidence of dryness.