hi my asparagus has gron in to a tree is this normal?

Leave the ferny fronds on until they start to go brown later in the year (then cut them down). As they are first year roots as in planted this year, you need to leave the greenery on in order for the roots to build up for growth next year. Normally new aspargus should be left at least 2 years before any harvest and then in the 3rd year, only a few shoots should be harvested.
Stake the ferny greenery but be careful not to spear the root itself.

This is what asparagus do in order to build up reserves for next years grow

As Nicky says, you will have to plant your asparagus soon. A fully developed asparagus plant has a huge root system extending over several metres, so you can't leave the plants in a pot too long. It's the root system that gives it all the strength to produce shoots over such a long season each year without being damaged as a plant.