Removing duplicate key should only remove 1 node

[jinusean]

const tree = new SplayTree()
const inputs: number[] = []

for (let number = 0; number < 10_000; number++) {
	for (let i = 0; i < 3; i++) {
		tree.insert(number)
		inputs.push(number)
	}
}

const shuffled = shuffle(inputs)
while (shuffled.length > 0) {
	const number = shuffled.pop()!
	tree.remove(number)
	if (tree.size !== tree.keys().length) {
		console.error('SIZE MISMATCH', number, 'size:', tree.size, 'keys:', tree.keys().length)
		break
	}
}

Results in

SIZE MISMATCH 5613 size: 29992 keys: 29991

Size is reduced by 1, by 2 nodes are removed.
There is no issue if the the numbers are not shuffled.