It's a mystery

As we head towards winter I'm looking forwards to spring and first things first I have a puzzle to solve.
I've been trying to identify this tree for 6 months now to no avail.  
These pictures were taken in the first week of May. It is a deciduous tree and the bark can be described as reddish brown and a little ridged.

Shape of tree

Flower formation

Flowers opening

Close up

Do you know what this is?