Ask Mr. Smarty Plants

Producing fruit is what most trees do, unless of course  you have a staminate (male) tree of a dioecious species. Otherwise, you need to select a tree with small, un-obnoxious fruit.

This article from the US Forest Service talks about the shapes of trees (scroll down to “Characteristic Shapes of Trees” about 3/4 of the way to the end). Your new tree could have a mushroom shaped crown, but that will be influenced by its interaction with the pecan tree.

For tree selection, I’m going to recommend the Texas Tree Planting Guide. This is an interactive web site from the Texas Forest Service that helps you pick trees based on your location, size of tree you want, and growing conditions. The simplest path is to use the “Express Tree Selector”. Answer the two questions , click on “view the best trees to plant” and you will get four reasonable choices. Check on the sizes and growth requirements to see which tree is best for you. By changing your search parameters, or using the "Custom Tree Selector", you can get other recommendations.

Here is a link to a previous answer that can also prove helpful.