I am a little confused by the wording of your post, but assuming that the trees are on your Strata Plan, it matters not whether they’re on Common Property or on any part of a Lot, all growth above the strata limit (vertical) is the responsibility of the Owners Corporation.
Individual Lot Owners do have a responsibility to keep the height of any and all trees / shrubs on their Lot below the strata limit, so provided they’ve been planted since the Registration of the Plan as opposed to being existing trees that were left in place during the Development, you may be able to obtain a contribution towards trimming costs from the Lot Owners concerned – but that would of course be voluntary.