read this decorating tip:
Fill in the inside of the tree (gaps, holes, etc., ) with all one color balls -- graduating the sizes from smallest at the top to medium, middle, and largest at the bottom. They will give the tree depth and reflect the lights. I use all white (clear) lights, red balls, then hang my collected ornaments and finish with an outside layer of white crocheted snowflakes. I decorated the Canadian tree at the Museum of Science and Industry's Christmas Around the World in Chicago for 20 years!