Looks like an oak gall. Formed on the twig of oak trees by a wasp.

Here is a link that might be useful: Scroll down to find info on oak gall

It's definitely not a gall. They have a yellow flesh inside them and they smell like they might be tasty! I've not been brave enough to try one though. Obviously I don't know what the tree is, but I do know it's not an oak.

Possibly one of the Strawberry Trees, Arbutus species. The fruit doesn't look exactly like the common Strawberry tree, Arbutus unedo, but could be a hybrid selection. Would it be possible to post a photo of the leaves and bark? Would help in identification.
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Kousa dogwood then.

Here is a link that might be useful: Kousa dogwood

It's a Kousa Dogwood. My trees look exactly like the ones on link.

Thanks!

The pulp is edible - and you may find it tasty; just 'massage' the fruit 'til it's soft, tear a hole in the skin(I just pull the stem out) and suck out the yellow-orange pulp.
Don't eat the skin - it's gritty and nasty-tasting. Beware of the little stone-like seeds - you could crack a tooth.