12 years ago when I moved into a new house a young two-stemmed oak sapling gave me the opportunity to create a young pollard. This was something I did partly because in English Nature I had been responsible for a magnificent wood in this area full of oak and hornbeam pollards, but also because I wanted to plant native deciduous trees for insects, and pollarding the tree every 2-3 years was one way to stop the sapling getting too big for the garden.
Pollards were created in the past by cutting trees above head height to give a crop of poles that could be used in the same way as coppice poles, but with the advantage that lifestock could be grazed under the trees without harming the young pollard shoots. Pollarding can prolong the life of such trees, and over time they can provide an excellent habitat for dead-wood invertebrates, fungi, bats and hole nesting birds.
Of course I will be long dead long before my tree could get to be anywhere near that interesting, but the management provides interesting patterns on the bark as successive branches are cut back every 2-3 years. The growth of the young stems produces shapes almost like molten wax as their bark grows over the stems cut a year or two previously. Which brings me to my silly mistake. Hanging that bird box between the two stems. In four years the branches have grown around the metal loop suspending the bird box, and fused to completely encase it, so the bird box has become a permanent fixture. Not quite what I intended!
All of which just goes to show how flexible tree growth can be.