Often in old movies and old t.v. shows as well, the trees seem to be of the same type/variety/species. I think I can offer some insight to why Hollywood move and t.v. trees always see to be perfectly shaped with open spaces and completely horizontal branches. The trees used are "Silver Tips" or "California Red Fir" trees. In the past, it was the Christmas tree that everyone seemed to use in California. With most old movies and t.v. show being filmed or taped in California... I am assuming that the prop departments simply chose the trees that were most readily available.
One of the few pleasant memories I have of living in California was that these "perfect" trees were still available in the 1990's, sold mostly on corner lots and lumber yards and garden centers. These trees were perfect for ornament hanging, open spaces for icicles to hang just right, and very fresh with long lasting qualities. However, even in the late 1990's these trees were being phased out for the more desirable, fuller, bushier and more fragrant Douglas, Noble, and Frasier firs. Well, times and tastes change. But, of the seven. Christmases I spend in CA, three of those were "Silver Tip" trees. Also, I will mention that the silver tips were very much more expensive than the more popular shorn and shaped trees from the tree farms. Their growing cycle is much longer than typical trees, and require the higher elevations of the mountains to grow, therefore harvesting and shipping were more expensive.
Just about every year since then I have researched the Internet for a grower in No. California, Oregon or Nevada that has these Hollywood Trees, however, I have never had any success in finding a grower willing to cut and ship just one tree.
Posted below are some pictures I have found of silver tip trees on Google Image search, some are of other silver tip tree appearances in the movies, others are from growers. Enjoy.
Silver Tip tid bit of the day... like I said, I had three of these wonderful trees over the years... and, being in California, one year I decided to go as tacky as possible and have the tree flocked... and flock it they did. By the time the flocking, lights, and ornaments were one, the poor thing was weighed down so much that most of the limbs pointed down to the floor. I recommend that if you are going to flock, then flock a stronger tree!
The Bishop's Wife: from http://www.beseaandscene.com/
A Summer's Place: http://www.imdb.com/
Holiday Inn: http://www.imdb.com/
Christmas In Connecticut: http://www.imdb.com/