Different growth but no graft site?

[Suziebun]

Can anyone tell me what is happening with this shrub tree? Its possibly a Lilac. Over the past two years its noticeably started to grow two different leaves and is now dropping those different leaves first.
THe different growth is all coming from the same trunk and there is no sign of any grafting.

Any ideas most welcome.

[Nicos]

Are you able to take a closer photo of the green leaves to help ID side?…then of a few fallen from the other side?