Simpsons Season 6, Episode 24: Lemon of Troy

After Marge teaches him about town pride, Bart becomes embroiled in a fight with a boy from the neighboring town of Shelbyville. The next day, Springfield's lemon tree is stolen by Shelbyville, and Bart leads Milhouse, Nelson, Martin, Todd, and Database to get it back. Bart learns that the tree is at an impound lot.