The apple symbolizes the Central Column and connects us with the Sefirot of the upper triangle of Zeir Anpin (Hesed, Gevura and Tiferet). The fruit has 3 colors: white – Right Column; red – Left Column; and green – Central Column. When the term Hakal Tapuhin Kadishin (the Field of Holy Apples) is mentioned, it refers to Malkhut in its ideal, perfect and balanced state.
According to The Zohar (Shemot) the apple connects to the upper triangle of Zeir Anpin while other fruits connect to Malkhut.