Jennifer Aniston’s annual Christmas tree-trimming party on Sunday night was a veritable who’s who in Hollywood. A-list friends Demi Moore, Ellen DeGeneres, Portia de Rossi, Ben Stiller, and Tobey Maguire all dressed up in their finest holiday attire for the bash at the rented Beverly Hills home the actress lives in with her fiancé Justin Theroux — but the fun wasn’t just for the adults. “The party was for both adults and children,” a source tells People. “Jen loves having children around and she always has fun activities planned for them. While the adults mingled, the younger guests were able to color and play games … Jen always puts a lot of effort into planning her holiday party.” And it wasn’t just famous people at the soiree. Many of Aniston’s employees also were in attendance because it’s also “a thank you party,” adds the source. “And she always gives them thoughtful gifts. Jen always asks her celebrity friends for charity donations instead of personal gifts.” The biggest star of the party though was the 10-foot noble fir the 43-year-old painstakingly selected at Mr. Greentrees in Beverly Hills — with a little help from her man. “She seemed very excited and happy about the tree,” the source revealed about Aniston, who is spending her second Christmas with Theroux. “[Justin] was very sweet to her and let her take her time to find the perfect tree. She found a beautiful one that she had delivered.”It was originally reported that Aniston’s bash was to celebrate her August engagement to Theroux, 41. Although that wasn’t the case, she’s certainly counting him as one of her many blessings in 2012! The twosome, who have yet to set a wedding date, “are doing really well together,” reveals the source. “Jen always seems so happy. Justin takes great care of her.”