You need a mattock, not a pickax. A mattock has one large blade turned at right angles to the handle and will get a big bite of earth when digging. The other blade is a sharp narrow ax type orientated in line with the handle and will be useful for cutting roots in the dirt.
Can't argue about the make. US stores started this offshoreing a long time ago. 40 years ago after marriage and building a house I got a mattock from an old time local hardware store and it was made in Spain. I haven't worn it out yet.
I'm suspicious of those yellow plastic handles. The one I saw broken in the warrenty bin at a HF store was plastic coated wood and the wood was a weak looking variety. During World War II the Japanese cut down every tree in the occupied zone and shipped it to Japan so how much replanting and growing of trees has gone on since then I don't know.
In selecting a mattock, or any other handled tool for that matter, hold the tool or handle by itself at eye level and sight along it. Reject any that are crooked or twisted, also reject any that have knots in them and ignore the clerk if he tries to tell you differently.
Maybe then the handle will stay straight, but wood has a mind of its own.
Google tree roots and maybe you will find something to help you in dealing with the variety of tree you have.
KEH