Fix: Compare ctx.value instead of ctx, fixes #2325 (#2326)

[zack-vii]

• Compare ctx.value instead of ctx, fixes python: after getting active tree with MDSplus.Tree(), setDefault() fails: "TreeNode must be in same tree" #2325

When instance of active tree is created (i.e. Tree()), comparing ctx
of node and tree result in node seeming to be from another tree