Is this berry poisonous
The tree in your photo is common buckthorn (Rhamnus cathartica). It is considered invasive and the fruit are considered toxic. If the berries are ingested they can cause stomach cramps and have a laxative effect.
By all means, remove it.
Control options are detailed in the following bulletins.
I hope this helps you out and thank you for using AaE.
Thanks for your help.
Using the information your provided I identified and removed 2 five foot male plants on my property and identified a few more of these plants I'll take out.
As for the one in the photo's, it has shoots arising on the property of two neighbors and has grown through power lines and up to a transformer, so I"ll have to speak to DTE, neighbors etc.
You are welcome!