Why didn't they bet a big banana? Why not a big orange? Why not a big plum? Because, again, the apple was the king of fruit, the mythical big reward. John J. Fitz Gerald was a handicapper. New York would always be "the big apple" to him, the biggest bet.
Below are just a few of the historical "bet a big (red) apple" published citations. The term was well established by 1900.
August 1847, The American Farmer, pg. 35:
Try it once and we'll bet you a big apple that you do it every year thereafter for the balance of your life.
April 1854, Prairie Farmer, pg. 154:
Without disposition other than to test the thing, I would willingly wager a "big apple" that not ten men, of those composing the Convention, can be found willing to plant this variety for market or family use, in place of the true Antwerp, Fastolf, or Orange.
27 August 1859, Spirit of the Times, pg. 343:
I have not heard from her morning, but will bet a big apple she never works in harness.
April 1871, Oliver Optic's Magazine, pg. 264:
I'd bet a big apple that Harry and I
Could eat them all up, one by one.
9 November 1886, Chicago Daily Tribune, pg. 4:
The Democrats have the House, but we will bet a big apple that they don't know what to do with it, now they've got it. -- New York Tribune.
4 June 1887, Chicago Daily Tribune, pg. 4:
...and we will bet a big red apple that Collier did not vote for Blaine, who has too many Irish friends to suit the English colony in Chicago.
25 October 1891, Boston Daily Globe, pg. 9 ad:
We will wager a big red apple that the prices attached to our thousand and one styles are as low or lower than the same quality of goods can be bought elsewhere.
10 September 1896, Chicago Daily Tribune, pg. 6:
Willie -- "I bet a big red apple with Tommy Tucker you didn't know. I've won it, hain't I?"
16 September 1897, The Dial, pg. 145:
We will bet a big red apple that anyone who reads "Patrins" can see what the effect of such an attitude has been on Miss Guiney.
14 March 1900, Colman's Rural World, "Missouri Apples at Manila," pg. 3:
I will bet a big red apple that Fred and his associates had a feast while the apples lasted.
13 February 1901, Puck, pg. 2:
And, what's more, I'll bet a big apple some of them plutocrats is organizin' an air-ship trust.
30 May 1903, Atlanta Constitution, pg. 4:
BIG RED APPLE
That Georgia Goes Demo-
cratic Next Year.
25 July 1903, Chicago Daily Tribune, pg. 5:
"I'll bet a big red apple that if James R. Keene had had nothing to do with the firm of Talbot J. Taylor & Co. they could have got all the money they needed."
1 March 1905, Chicago Daily Tribune, pg. 12:
"I don't believe the May deal is over," said R. D. Richardson, "and will bet a big red apple that May wheat will yet sell higher than it has done so far."
22 September 1907, Boston Daily Globe, pg. 24:
The Whitney plotters said yesterday that things were looking good to them in ward 20 and they would bet a big apple that some of the "Red Devil" candidates for delegate to the state convention would fall by the wayside next Tuesday.
16 October 1907, Los Angeles
You can wager a big red apple that Miss Flagg will not recommend half-cooked restaurant meals, nor Mrs. Stilson a barrel of ostrich feathers on the hat.
8 January 1908, Boston Daily Globe, pg. 7:
The spokesman of the Williams-Kiley-Feeney state committee alliance said last night that he would bet a big red apple to a peanut that McNary wouldn't have a baker's dozen at his meeting.
2 November 1908, Chicago Daily Tribune, pg. 8:
I will bet a big apple that if Mr. Bryan should be elected your salary will be reduced 25 per cent within twelve months after his election.
16 November 1908, Los Angeles Times, pg. 16:
We will bet a big apple that there will be many men and women in its ranks
15 July 1909, Los Angeles Times, pg. II4:
But we'll wager a big red apple that it was not at the rate of a dollar a word.
22 December 1911, Los Angeles
Saw a man on Broadway the other day try to stop a street car by waving an umbrella at it. We will wager a big red apple that he was from the East.
2 June 1914, New York Times, pg. 3:
"Mayor Mitchel may be down to see me at Oyster Bay," he (Colonel Roosevelt -- ed.) added. "If he comes I would bet a big red apple that we would talk on municipal affairs only rather than State politics."
9 July 1913, Puck, pg. 3:
THE GENTLEMAN FROM KANSAS (proudly). -- I just wish we had one o' them machines to hum! I'll bet a big apple I'd get the next nomination for Congress from our district!
26 November 1924, Washington Post, pg. 6:
We stand ready to bet a big red apple against the hole in a doughnut
26 February 1941, Los Angeles Times, Hedda Hopper's Hollywood, pg. A11:
His new one, "The Lady Eve," will wind up as THE comedy of the year, and I'll bet you a big red apple on it.