Microchip has a lost cost programmer called PICkit 2 which is a programmer and development platform. The PICKit 2 starter kit is available from Microchip Direct or several other sources (mouser.com or digikey.com)
Microchip released the schematics and source code for the PICkit 2 programmer so there are also several other programmers capable of programming the PIC processors based on the design. Below are a couple of links. Also if you search the web for PIC programmers you will find lots of low cost alternatives. Just make sure you can program the PIC used in the Xmas Tree. If you are new to PIC processors you may want to stick with the PICkit 2 or a similar debug/development platform.