Gather twigs and branches.
Soak them with hot water and about 1/2 cup of bleach.
Rinse them off, and set them out on newspaper to dry.
Drill a hole in a couple of pieces of scrap wood to use as the base of the tree.
Use a bit of gel stain to darken the wood.
Hot glue the trees into the bases so they can stand upright.
Hot glue similar sized twigs several inches up the tree trunk.
Leave enough room to show some of the bottom of the trunk.
Glue more twigs above the first layer, making sure that they overlap the first set.
Repeat until you reach the top.