tree
杝 is a rare kanji that refers to a type of tree. Its standalone meaning is simply 'tree'.
杝 combines 木 (tree) with 也, which likely contributes the sound. The exact historical development is uncertain.
The left side is a tree 木, and the right side 也 looks like a twisted branch. Picture a tree with a distinctive twisted branch: 杝 is a tree.
For チ, imagine a tree with a twisted branch that looks like the letter 'T': T -> チ, and the tree is 杝.